diff --git a/src/program.ts b/src/program.ts
index c333b36054..3a9dfb09a0 100644
--- a/src/program.ts
+++ b/src/program.ts
@@ -3007,10 +3007,30 @@ export abstract class DeclaredElement extends Element {
   isCompatibleOverride(base: DeclaredElement): bool {
     var self: DeclaredElement = this; // TS
     var kind = self.kind;
+    var checkCompatibleOverride = false;
     if (kind == base.kind) {
       switch (kind) {
+        case ElementKind.FUNCTION_PROTOTYPE : {
+          let selfFunction = this.program.resolver.resolveFunction(<FunctionPrototype>self, null);
+          if (!selfFunction) return false;
+          let baseFunction = this.program.resolver.resolveFunction(<FunctionPrototype>base, null);
+          if (!baseFunction) return false;
+          self = selfFunction;
+          base = baseFunction;
+          checkCompatibleOverride = true;
+          // fall-through
+        }
         case ElementKind.FUNCTION: {
-          return (<Function>self).signature.isAssignableTo((<Function>base).signature);
+          return (<Function>self).signature.isAssignableTo((<Function>base).signature, checkCompatibleOverride);
+        }
+        case ElementKind.PROPERTY_PROTOTYPE: {
+          let selfProperty = this.program.resolver.resolveProperty(<PropertyPrototype>self);
+          if (!selfProperty) return false;
+          let baseProperty = this.program.resolver.resolveProperty(<PropertyPrototype>base);
+          if (!baseProperty) return false;
+          self = selfProperty;
+          base = baseProperty;
+          // fall-through
         }
         case ElementKind.PROPERTY: {
           let selfProperty = <Property>self;
@@ -3018,7 +3038,7 @@ export abstract class DeclaredElement extends Element {
           let selfGetter = selfProperty.getterInstance;
           let baseGetter = baseProperty.getterInstance;
           if (selfGetter) {
-            if (!baseGetter || !selfGetter.signature.isAssignableTo(baseGetter.signature)) {
+            if (!baseGetter || !selfGetter.signature.isAssignableTo(baseGetter.signature, true)) {
               return false;
             }
           } else if (baseGetter) {
@@ -3027,7 +3047,7 @@ export abstract class DeclaredElement extends Element {
           let selfSetter = selfProperty.setterInstance;
           let baseSetter = baseProperty.setterInstance;
           if (selfSetter) {
-            if (!baseSetter || !selfSetter.signature.isAssignableTo(baseSetter.signature)) {
+            if (!baseSetter || !selfSetter.signature.isAssignableTo(baseSetter.signature, true)) {
               return false;
             }
           } else if (baseSetter) {
@@ -3035,6 +3055,10 @@ export abstract class DeclaredElement extends Element {
           }
           return true;
         }
+        // TODO: Implement properties overriding fields and vice-versa. Challenge is that anything overridable requires
+        // a virtual stub, but fields aren't functions. Either all (such) fields should become property-like, with a
+        // getter and a setter that can participate as a virtual stub, or it's allowed one-way, with fields integrated
+        // into what can be a virtual stub as get=load and set=store, then not necessarily with own accessor functions.
       }
     }
     return false;
@@ -4294,6 +4318,11 @@ export class Class extends TypedElement {
     );
   }
 
+  /** Tests if this is an interface. */
+  get isInterface(): bool {
+    return this.kind == ElementKind.INTERFACE;
+  }
+
   /** Constructs a new class. */
   constructor(
     /** Name incl. type parameters, i.e. `Foo<i32>`. */
diff --git a/src/types.ts b/src/types.ts
index 5c6c071b96..9a2f0361d6 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -502,6 +502,27 @@ export class Type {
     return this.kind == target.kind;
   }
 
+  /** Tests if this type can extend or implement the given type. */
+  canExtendOrImplement(base: Type): bool {
+    // Both must be class types
+    var thisClass = this.getClass();
+    var baseClass = base.getClass();
+    if (!thisClass || !baseClass) return false;
+    // Both types must be either managed or unmanaged
+    if (this.isManaged != base.isManaged) return false;
+    // Both types must be either internal or external references
+    if (this.isInternalReference) {
+      if (!base.isInternalReference) return false;
+    } else if (this.isExternalReference) {
+      if (!base.isExternalReference) return false;
+    } else {
+      return false;
+    }
+    // Interfaces can only extend interfaces
+    if (thisClass.isInterface && !baseClass.isInterface) return false;
+    return true;
+  }
+
   /** Determines the common denominator type of two types, if there is any. */
   static commonDenominator(left: Type, right: Type, signednessIsImportant: bool): Type | null {
     if (right.isAssignableTo(left, signednessIsImportant)) return left;
@@ -926,17 +947,27 @@ export class Signature {
   }
 
   /** Tests if a value of this function type is assignable to a target of the specified function type. */
-  isAssignableTo(target: Signature): bool {
-
-    // check `this` type
+  isAssignableTo(target: Signature, checkCompatibleOverride: bool = false): bool {
     var thisThisType = this.thisType;
     var targetThisType = target.thisType;
-    if (thisThisType) {
-      if (!targetThisType || !thisThisType.isAssignableTo(targetThisType)) {
+    if (!checkCompatibleOverride) {
+      // check exact `this` type
+      if (thisThisType) {
+        if (!targetThisType || !thisThisType.isAssignableTo(targetThisType)) {
+          return false;
+        }
+      } else if (targetThisType) {
+        return false;
+      }
+    } else {
+      // check kind of `this` type
+      if (thisThisType) {
+        if (!targetThisType || !thisThisType.canExtendOrImplement(targetThisType)) {
+          return false;
+        }
+      } else if (targetThisType) {
         return false;
       }
-    } else if (targetThisType) {
-      return false;
     }
 
     // check rest parameter
diff --git a/tests/compiler/class-implements.debug.wat b/tests/compiler/class-implements.debug.wat
index 930954ad61..7406a835b8 100644
--- a/tests/compiler/class-implements.debug.wat
+++ b/tests/compiler/class-implements.debug.wat
@@ -1,6 +1,6 @@
 (module
- (type $i32_i32_=>_none (func (param i32 i32)))
  (type $i32_=>_i32 (func (param i32) (result i32)))
+ (type $i32_i32_=>_none (func (param i32 i32)))
  (type $i32_=>_none (func (param i32)))
  (type $none_=>_none (func))
  (type $i32_i32_=>_i32 (func (param i32 i32) (result i32)))
@@ -25,10 +25,15 @@
  (global $~lib/native/ASC_LOW_MEMORY_LIMIT i32 (i32.const 0))
  (global $class-implements/a (mut i32) (i32.const 0))
  (global $class-implements/c (mut i32) (i32.const 0))
+ (global $class-implements/d (mut i32) (i32.const 0))
+ (global $class-implements/e (mut i32) (i32.const 0))
+ (global $class-implements/f (mut i32) (i32.const 0))
+ (global $class-implements/g (mut i32) (i32.const 0))
+ (global $class-implements/h (mut i32) (i32.const 0))
  (global $~lib/rt/__rtti_base i32 (i32.const 480))
- (global $~lib/memory/__data_end i32 (i32.const 540))
- (global $~lib/memory/__stack_pointer (mut i32) (i32.const 16924))
- (global $~lib/memory/__heap_base i32 (i32.const 16924))
+ (global $~lib/memory/__data_end i32 (i32.const 572))
+ (global $~lib/memory/__stack_pointer (mut i32) (i32.const 16956))
+ (global $~lib/memory/__heap_base i32 (i32.const 16956))
  (memory $0 1)
  (data (i32.const 12) "<\00\00\00\00\00\00\00\00\00\00\00\01\00\00\00(\00\00\00A\00l\00l\00o\00c\00a\00t\00i\00o\00n\00 \00t\00o\00o\00 \00l\00a\00r\00g\00e\00\00\00\00\00")
  (data (i32.const 76) "<\00\00\00\00\00\00\00\00\00\00\00\01\00\00\00 \00\00\00~\00l\00i\00b\00/\00r\00t\00/\00i\00t\00c\00m\00s\00.\00t\00s\00\00\00\00\00\00\00\00\00\00\00\00\00")
@@ -39,7 +44,7 @@
  (data (i32.const 320) "\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00")
  (data (i32.const 348) "<\00\00\00\00\00\00\00\00\00\00\00\01\00\00\00\1e\00\00\00~\00l\00i\00b\00/\00r\00t\00/\00t\00l\00s\00f\00.\00t\00s\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00")
  (data (i32.const 412) "<\00\00\00\00\00\00\00\00\00\00\00\01\00\00\00&\00\00\00c\00l\00a\00s\00s\00-\00i\00m\00p\00l\00e\00m\00e\00n\00t\00s\00.\00t\00s\00\00\00\00\00\00\00")
- (data (i32.const 480) "\07\00\00\00 \00\00\00\00\00\00\00 \00\00\00\00\00\00\00\00\00\00\00\00\00\00\00 \00\00\00\00\00\00\00 \00\00\00\00\00\00\00 \00\00\00\06\00\00\00 \00\00\00\00\00\00\00")
+ (data (i32.const 480) "\0b\00\00\00 \00\00\00\00\00\00\00 \00\00\00\00\00\00\00\00\00\00\00\00\00\00\00 \00\00\00\00\00\00\00 \00\00\00\00\00\00\00 \00\00\00\06\00\00\00 \00\00\00\00\00\00\00 \00\00\00\00\00\00\00 \00\00\00\00\00\00\00 \00\00\00\07\00\00\00 \00\00\00\07\00\00\00")
  (table $0 1 1 funcref)
  (elem $0 (i32.const 1))
  (export "memory" (memory $0))
@@ -2122,6 +2127,89 @@
  (func $class-implements/C#foo (param $this i32) (result i32)
   i32.const 2
  )
+ (func $class-implements/D#foo (param $this i32) (result i32)
+  i32.const 3
+ )
+ (func $class-implements/F#foo (param $this i32) (result i32)
+  i32.const 4
+ )
+ (func $class-implements/I#foo (param $this i32) (result i32)
+  unreachable
+ )
+ (func $class-implements/D#foo@virtual (param $0 i32) (result i32)
+  (local $1 i32)
+  block $default
+   block $case0
+    local.get $0
+    i32.const 8
+    i32.sub
+    i32.load $0
+    local.set $1
+    local.get $1
+    i32.const 10
+    i32.eq
+    br_if $case0
+    br $default
+   end
+   local.get $0
+   call $class-implements/F#foo
+   return
+  end
+  local.get $0
+  call $class-implements/D#foo
+ )
+ (func $class-implements/I#foo@virtual (param $0 i32) (result i32)
+  (local $1 i32)
+  block $default
+   block $case3
+    block $case2
+     block $case1
+      block $case0
+       local.get $0
+       i32.const 8
+       i32.sub
+       i32.load $0
+       local.set $1
+       local.get $1
+       i32.const 3
+       i32.eq
+       br_if $case0
+       local.get $1
+       i32.const 5
+       i32.eq
+       br_if $case1
+       local.get $1
+       i32.const 7
+       i32.eq
+       br_if $case2
+       local.get $1
+       i32.const 9
+       i32.eq
+       br_if $case2
+       local.get $1
+       i32.const 10
+       i32.eq
+       br_if $case3
+       br $default
+      end
+      local.get $0
+      call $class-implements/A#foo
+      return
+     end
+     local.get $0
+     call $class-implements/C#foo
+     return
+    end
+    local.get $0
+    call $class-implements/D#foo
+    return
+   end
+   local.get $0
+   call $class-implements/F#foo
+   return
+  end
+  unreachable
+ )
  (func $~lib/rt/__visit_globals (param $0 i32)
   (local $1 i32)
   global.get $class-implements/a
@@ -2138,6 +2226,41 @@
    local.get $0
    call $~lib/rt/itcms/__visit
   end
+  global.get $class-implements/d
+  local.tee $1
+  if
+   local.get $1
+   local.get $0
+   call $~lib/rt/itcms/__visit
+  end
+  global.get $class-implements/e
+  local.tee $1
+  if
+   local.get $1
+   local.get $0
+   call $~lib/rt/itcms/__visit
+  end
+  global.get $class-implements/f
+  local.tee $1
+  if
+   local.get $1
+   local.get $0
+   call $~lib/rt/itcms/__visit
+  end
+  global.get $class-implements/g
+  local.tee $1
+  if
+   local.get $1
+   local.get $0
+   call $~lib/rt/itcms/__visit
+  end
+  global.get $class-implements/h
+  local.tee $1
+  if
+   local.get $1
+   local.get $0
+   call $~lib/rt/itcms/__visit
+  end
   i32.const 224
   local.get $0
   call $~lib/rt/itcms/__visit
@@ -2158,26 +2281,38 @@
  )
  (func $~lib/rt/__visit_members (param $0 i32) (param $1 i32)
   block $invalid
-   block $class-implements/B
-    block $class-implements/C
-     block $class-implements/I
-      block $class-implements/A
-       block $~lib/arraybuffer/ArrayBufferView
-        block $~lib/string/String
-         block $~lib/arraybuffer/ArrayBuffer
-          local.get $0
-          i32.const 8
-          i32.sub
-          i32.load $0
-          br_table $~lib/arraybuffer/ArrayBuffer $~lib/string/String $~lib/arraybuffer/ArrayBufferView $class-implements/A $class-implements/I $class-implements/C $class-implements/B $invalid
+   block $class-implements/F
+    block $class-implements/E
+     block $class-implements/J
+      block $class-implements/D
+       block $class-implements/B
+        block $class-implements/C
+         block $class-implements/I
+          block $class-implements/A
+           block $~lib/arraybuffer/ArrayBufferView
+            block $~lib/string/String
+             block $~lib/arraybuffer/ArrayBuffer
+              local.get $0
+              i32.const 8
+              i32.sub
+              i32.load $0
+              br_table $~lib/arraybuffer/ArrayBuffer $~lib/string/String $~lib/arraybuffer/ArrayBufferView $class-implements/A $class-implements/I $class-implements/C $class-implements/B $class-implements/D $class-implements/J $class-implements/E $class-implements/F $invalid
+             end
+             return
+            end
+            return
+           end
+           local.get $0
+           local.get $1
+           call $~lib/arraybuffer/ArrayBufferView~visit
+           return
+          end
+          return
          end
          return
         end
         return
        end
-       local.get $0
-       local.get $1
-       call $~lib/arraybuffer/ArrayBufferView~visit
        return
       end
       return
@@ -2198,8 +2333,8 @@
   global.get $~lib/memory/__data_end
   i32.lt_s
   if
-   i32.const 16944
-   i32.const 16992
+   i32.const 16976
+   i32.const 17024
    i32.const 1
    i32.const 1
    call $~lib/builtins/abort
@@ -2249,7 +2384,7 @@
   if
    i32.const 0
    i32.const 432
-   i32.const 10
+   i32.const 14
    i32.const 1
    call $~lib/builtins/abort
    unreachable
@@ -2270,7 +2405,112 @@
   if
    i32.const 0
    i32.const 432
-   i32.const 20
+   i32.const 24
+   i32.const 1
+   call $~lib/builtins/abort
+   unreachable
+  end
+  i32.const 0
+  call $class-implements/D#constructor
+  global.set $class-implements/d
+  global.get $class-implements/d
+  local.set $0
+  global.get $~lib/memory/__stack_pointer
+  local.get $0
+  i32.store $0
+  local.get $0
+  call $class-implements/D#foo@virtual
+  i32.const 3
+  i32.eq
+  i32.eqz
+  if
+   i32.const 0
+   i32.const 432
+   i32.const 31
+   i32.const 1
+   call $~lib/builtins/abort
+   unreachable
+  end
+  i32.const 0
+  call $class-implements/E#constructor
+  global.set $class-implements/e
+  global.get $class-implements/e
+  local.set $0
+  global.get $~lib/memory/__stack_pointer
+  local.get $0
+  i32.store $0
+  local.get $0
+  call $class-implements/D#foo@virtual
+  i32.const 3
+  i32.eq
+  i32.eqz
+  if
+   i32.const 0
+   i32.const 432
+   i32.const 37
+   i32.const 1
+   call $~lib/builtins/abort
+   unreachable
+  end
+  i32.const 0
+  call $class-implements/F#constructor
+  global.set $class-implements/f
+  global.get $class-implements/f
+  local.set $0
+  global.get $~lib/memory/__stack_pointer
+  local.get $0
+  i32.store $0
+  local.get $0
+  call $class-implements/F#foo
+  i32.const 4
+  i32.eq
+  i32.eqz
+  if
+   i32.const 0
+   i32.const 432
+   i32.const 44
+   i32.const 1
+   call $~lib/builtins/abort
+   unreachable
+  end
+  i32.const 0
+  call $class-implements/F#constructor
+  global.set $class-implements/g
+  global.get $class-implements/g
+  local.set $0
+  global.get $~lib/memory/__stack_pointer
+  local.get $0
+  i32.store $0
+  local.get $0
+  call $class-implements/D#foo@virtual
+  i32.const 4
+  i32.eq
+  i32.eqz
+  if
+   i32.const 0
+   i32.const 432
+   i32.const 47
+   i32.const 1
+   call $~lib/builtins/abort
+   unreachable
+  end
+  i32.const 0
+  call $class-implements/F#constructor
+  global.set $class-implements/h
+  global.get $class-implements/h
+  local.set $0
+  global.get $~lib/memory/__stack_pointer
+  local.get $0
+  i32.store $0
+  local.get $0
+  call $class-implements/I#foo@virtual
+  i32.const 4
+  i32.eq
+  i32.eqz
+  if
+   i32.const 0
+   i32.const 432
+   i32.const 50
    i32.const 1
    call $~lib/builtins/abort
    unreachable
@@ -2369,4 +2609,98 @@
   global.set $~lib/memory/__stack_pointer
   local.get $1
  )
+ (func $class-implements/D#constructor (param $this i32) (result i32)
+  (local $1 i32)
+  global.get $~lib/memory/__stack_pointer
+  i32.const 4
+  i32.sub
+  global.set $~lib/memory/__stack_pointer
+  call $~stack_check
+  global.get $~lib/memory/__stack_pointer
+  i32.const 0
+  i32.store $0
+  local.get $this
+  i32.eqz
+  if
+   global.get $~lib/memory/__stack_pointer
+   i32.const 0
+   i32.const 7
+   call $~lib/rt/itcms/__new
+   local.tee $this
+   i32.store $0
+  end
+  local.get $this
+  local.set $1
+  global.get $~lib/memory/__stack_pointer
+  i32.const 4
+  i32.add
+  global.set $~lib/memory/__stack_pointer
+  local.get $1
+ )
+ (func $class-implements/E#constructor (param $this i32) (result i32)
+  (local $1 i32)
+  global.get $~lib/memory/__stack_pointer
+  i32.const 4
+  i32.sub
+  global.set $~lib/memory/__stack_pointer
+  call $~stack_check
+  global.get $~lib/memory/__stack_pointer
+  i32.const 0
+  i32.store $0
+  local.get $this
+  i32.eqz
+  if
+   global.get $~lib/memory/__stack_pointer
+   i32.const 0
+   i32.const 9
+   call $~lib/rt/itcms/__new
+   local.tee $this
+   i32.store $0
+  end
+  global.get $~lib/memory/__stack_pointer
+  local.get $this
+  call $class-implements/D#constructor
+  local.tee $this
+  i32.store $0
+  local.get $this
+  local.set $1
+  global.get $~lib/memory/__stack_pointer
+  i32.const 4
+  i32.add
+  global.set $~lib/memory/__stack_pointer
+  local.get $1
+ )
+ (func $class-implements/F#constructor (param $this i32) (result i32)
+  (local $1 i32)
+  global.get $~lib/memory/__stack_pointer
+  i32.const 4
+  i32.sub
+  global.set $~lib/memory/__stack_pointer
+  call $~stack_check
+  global.get $~lib/memory/__stack_pointer
+  i32.const 0
+  i32.store $0
+  local.get $this
+  i32.eqz
+  if
+   global.get $~lib/memory/__stack_pointer
+   i32.const 0
+   i32.const 10
+   call $~lib/rt/itcms/__new
+   local.tee $this
+   i32.store $0
+  end
+  global.get $~lib/memory/__stack_pointer
+  local.get $this
+  call $class-implements/D#constructor
+  local.tee $this
+  i32.store $0
+  local.get $this
+  local.set $1
+  global.get $~lib/memory/__stack_pointer
+  i32.const 4
+  i32.add
+  global.set $~lib/memory/__stack_pointer
+  local.get $1
+ )
 )
diff --git a/tests/compiler/class-implements.release.wat b/tests/compiler/class-implements.release.wat
index 7545bad8a7..154645f85d 100644
--- a/tests/compiler/class-implements.release.wat
+++ b/tests/compiler/class-implements.release.wat
@@ -1,11 +1,11 @@
 (module
  (type $none_=>_none (func))
- (type $i32_i32_=>_none (func (param i32 i32)))
  (type $i32_=>_i32 (func (param i32) (result i32)))
+ (type $i32_i32_=>_none (func (param i32 i32)))
+ (type $none_=>_i32 (func (result i32)))
  (type $i32_=>_none (func (param i32)))
  (type $i32_i32_i32_i32_=>_none (func (param i32 i32 i32 i32)))
  (type $i32_i32_i32_=>_none (func (param i32 i32 i32)))
- (type $none_=>_i32 (func (result i32)))
  (import "env" "abort" (func $~lib/builtins/abort (param i32 i32 i32 i32)))
  (global $~lib/rt/itcms/total (mut i32) (i32.const 0))
  (global $~lib/rt/itcms/threshold (mut i32) (i32.const 0))
@@ -19,7 +19,12 @@
  (global $~lib/rt/tlsf/ROOT (mut i32) (i32.const 0))
  (global $class-implements/a (mut i32) (i32.const 0))
  (global $class-implements/c (mut i32) (i32.const 0))
- (global $~lib/memory/__stack_pointer (mut i32) (i32.const 17948))
+ (global $class-implements/d (mut i32) (i32.const 0))
+ (global $class-implements/e (mut i32) (i32.const 0))
+ (global $class-implements/f (mut i32) (i32.const 0))
+ (global $class-implements/g (mut i32) (i32.const 0))
+ (global $class-implements/h (mut i32) (i32.const 0))
+ (global $~lib/memory/__stack_pointer (mut i32) (i32.const 17980))
  (memory $0 1)
  (data (i32.const 1036) "<")
  (data (i32.const 1048) "\01\00\00\00(\00\00\00A\00l\00l\00o\00c\00a\00t\00i\00o\00n\00 \00t\00o\00o\00 \00l\00a\00r\00g\00e")
@@ -33,8 +38,8 @@
  (data (i32.const 1384) "\01\00\00\00\1e\00\00\00~\00l\00i\00b\00/\00r\00t\00/\00t\00l\00s\00f\00.\00t\00s")
  (data (i32.const 1436) "<")
  (data (i32.const 1448) "\01\00\00\00&\00\00\00c\00l\00a\00s\00s\00-\00i\00m\00p\00l\00e\00m\00e\00n\00t\00s\00.\00t\00s")
- (data (i32.const 1504) "\07\00\00\00 \00\00\00\00\00\00\00 ")
- (data (i32.const 1532) " \00\00\00\00\00\00\00 \00\00\00\00\00\00\00 \00\00\00\06\00\00\00 ")
+ (data (i32.const 1504) "\0b\00\00\00 \00\00\00\00\00\00\00 ")
+ (data (i32.const 1532) " \00\00\00\00\00\00\00 \00\00\00\00\00\00\00 \00\00\00\06\00\00\00 \00\00\00\00\00\00\00 \00\00\00\00\00\00\00 \00\00\00\00\00\00\00 \00\00\00\07\00\00\00 \00\00\00\07")
  (export "memory" (memory $0))
  (start $~start)
  (func $~lib/rt/itcms/visitRoots
@@ -52,6 +57,36 @@
    local.get $0
    call $byn-split-outlined-A$~lib/rt/itcms/__visit
   end
+  global.get $class-implements/d
+  local.tee $0
+  if
+   local.get $0
+   call $byn-split-outlined-A$~lib/rt/itcms/__visit
+  end
+  global.get $class-implements/e
+  local.tee $0
+  if
+   local.get $0
+   call $byn-split-outlined-A$~lib/rt/itcms/__visit
+  end
+  global.get $class-implements/f
+  local.tee $0
+  if
+   local.get $0
+   call $byn-split-outlined-A$~lib/rt/itcms/__visit
+  end
+  global.get $class-implements/g
+  local.tee $0
+  if
+   local.get $0
+   call $byn-split-outlined-A$~lib/rt/itcms/__visit
+  end
+  global.get $class-implements/h
+  local.tee $0
+  if
+   local.get $0
+   call $byn-split-outlined-A$~lib/rt/itcms/__visit
+  end
   i32.const 1248
   call $byn-split-outlined-A$~lib/rt/itcms/__visit
   i32.const 1056
@@ -625,10 +660,10 @@
   if
    unreachable
   end
-  i32.const 17952
+  i32.const 17984
   i32.const 0
   i32.store $0
-  i32.const 19520
+  i32.const 19552
   i32.const 0
   i32.store $0
   loop $for-loop|0
@@ -639,7 +674,7 @@
     local.get $0
     i32.const 2
     i32.shl
-    i32.const 17952
+    i32.const 17984
     i32.add
     i32.const 0
     i32.store $0 offset=4
@@ -657,7 +692,7 @@
       i32.add
       i32.const 2
       i32.shl
-      i32.const 17952
+      i32.const 17984
       i32.add
       i32.const 0
       i32.store $0 offset=96
@@ -675,13 +710,13 @@
     br $for-loop|0
    end
   end
-  i32.const 17952
-  i32.const 19524
+  i32.const 17984
+  i32.const 19556
   memory.size $0
   i32.const 16
   i32.shl
   call $~lib/rt/tlsf/addMemory
-  i32.const 17952
+  i32.const 17984
   global.set $~lib/rt/tlsf/ROOT
  )
  (func $~lib/rt/itcms/step (result i32)
@@ -766,7 +801,7 @@
      local.set $0
      loop $while-continue|0
       local.get $0
-      i32.const 17948
+      i32.const 17980
       i32.lt_u
       if
        local.get $0
@@ -866,7 +901,7 @@
      unreachable
     end
     local.get $0
-    i32.const 17948
+    i32.const 17980
     i32.lt_u
     if
      local.get $0
@@ -889,7 +924,7 @@
      i32.const 4
      i32.add
      local.tee $0
-     i32.const 17948
+     i32.const 17980
      i32.ge_u
      if
       global.get $~lib/rt/tlsf/ROOT
@@ -1243,30 +1278,42 @@
  )
  (func $~lib/rt/__visit_members (param $0 i32)
   block $invalid
-   block $class-implements/B
-    block $class-implements/C
-     block $class-implements/I
-      block $class-implements/A
-       block $~lib/arraybuffer/ArrayBufferView
-        block $~lib/string/String
-         block $~lib/arraybuffer/ArrayBuffer
-          local.get $0
-          i32.const 8
-          i32.sub
-          i32.load $0
-          br_table $~lib/arraybuffer/ArrayBuffer $~lib/string/String $~lib/arraybuffer/ArrayBufferView $class-implements/A $class-implements/I $class-implements/C $class-implements/B $invalid
+   block $class-implements/F
+    block $class-implements/E
+     block $class-implements/J
+      block $class-implements/D
+       block $class-implements/B
+        block $class-implements/C
+         block $class-implements/I
+          block $class-implements/A
+           block $~lib/arraybuffer/ArrayBufferView
+            block $~lib/string/String
+             block $~lib/arraybuffer/ArrayBuffer
+              local.get $0
+              i32.const 8
+              i32.sub
+              i32.load $0
+              br_table $~lib/arraybuffer/ArrayBuffer $~lib/string/String $~lib/arraybuffer/ArrayBufferView $class-implements/A $class-implements/I $class-implements/C $class-implements/B $class-implements/D $class-implements/J $class-implements/E $class-implements/F $invalid
+             end
+             return
+            end
+            return
+           end
+           local.get $0
+           i32.load $0
+           local.tee $0
+           if
+            local.get $0
+            call $byn-split-outlined-A$~lib/rt/itcms/__visit
+           end
+           return
+          end
+          return
          end
          return
         end
         return
        end
-       local.get $0
-       i32.load $0
-       local.tee $0
-       if
-        local.get $0
-        call $byn-split-outlined-A$~lib/rt/itcms/__visit
-       end
        return
       end
       return
@@ -1288,7 +1335,7 @@
   global.set $~lib/memory/__stack_pointer
   block $folding-inner0
    global.get $~lib/memory/__stack_pointer
-   i32.const 1564
+   i32.const 1596
    i32.lt_s
    br_if $folding-inner0
    global.get $~lib/memory/__stack_pointer
@@ -1298,7 +1345,7 @@
    memory.size $0
    i32.const 16
    i32.shl
-   i32.const 17948
+   i32.const 17980
    i32.sub
    i32.const 1
    i32.shr_u
@@ -1332,7 +1379,7 @@
    i32.sub
    global.set $~lib/memory/__stack_pointer
    global.get $~lib/memory/__stack_pointer
-   i32.const 1564
+   i32.const 1596
    i32.lt_s
    br_if $folding-inner0
    global.get $~lib/memory/__stack_pointer
@@ -1358,7 +1405,7 @@
    i32.sub
    global.set $~lib/memory/__stack_pointer
    global.get $~lib/memory/__stack_pointer
-   i32.const 1564
+   i32.const 1596
    i32.lt_s
    br_if $folding-inner0
    global.get $~lib/memory/__stack_pointer
@@ -1376,7 +1423,7 @@
    i32.sub
    global.set $~lib/memory/__stack_pointer
    global.get $~lib/memory/__stack_pointer
-   i32.const 1564
+   i32.const 1596
    i32.lt_s
    br_if $folding-inner0
    global.get $~lib/memory/__stack_pointer
@@ -1407,19 +1454,255 @@
    global.get $~lib/memory/__stack_pointer
    global.get $class-implements/c
    i32.store $0
+   i32.const 0
+   call $class-implements/D#constructor
+   global.set $class-implements/d
+   block $__inlined_func$class-implements/D#foo@virtual (result i32)
+    global.get $~lib/memory/__stack_pointer
+    global.get $class-implements/d
+    local.tee $0
+    i32.store $0
+    i32.const 4
+    local.get $0
+    i32.const 8
+    i32.sub
+    i32.load $0
+    i32.const 10
+    i32.eq
+    br_if $__inlined_func$class-implements/D#foo@virtual
+    drop
+    i32.const 3
+   end
+   i32.const 3
+   i32.ne
+   if
+    i32.const 0
+    i32.const 1456
+    i32.const 31
+    i32.const 1
+    call $~lib/builtins/abort
+    unreachable
+   end
+   global.get $~lib/memory/__stack_pointer
+   i32.const 4
+   i32.sub
+   global.set $~lib/memory/__stack_pointer
+   global.get $~lib/memory/__stack_pointer
+   i32.const 1596
+   i32.lt_s
+   br_if $folding-inner0
+   global.get $~lib/memory/__stack_pointer
+   local.tee $0
+   i32.const 0
+   i32.store $0
+   local.get $0
+   i32.const 9
+   call $~lib/rt/itcms/__new
+   local.tee $0
+   i32.store $0
+   global.get $~lib/memory/__stack_pointer
+   local.get $0
+   call $class-implements/D#constructor
+   local.tee $0
+   i32.store $0
+   global.get $~lib/memory/__stack_pointer
+   i32.const 4
+   i32.add
+   global.set $~lib/memory/__stack_pointer
+   local.get $0
+   global.set $class-implements/e
+   block $__inlined_func$class-implements/D#foo@virtual9 (result i32)
+    global.get $~lib/memory/__stack_pointer
+    global.get $class-implements/e
+    local.tee $0
+    i32.store $0
+    i32.const 4
+    local.get $0
+    i32.const 8
+    i32.sub
+    i32.load $0
+    i32.const 10
+    i32.eq
+    br_if $__inlined_func$class-implements/D#foo@virtual9
+    drop
+    i32.const 3
+   end
+   i32.const 3
+   i32.ne
+   if
+    i32.const 0
+    i32.const 1456
+    i32.const 37
+    i32.const 1
+    call $~lib/builtins/abort
+    unreachable
+   end
+   call $class-implements/F#constructor
+   global.set $class-implements/f
+   global.get $~lib/memory/__stack_pointer
+   global.get $class-implements/f
+   i32.store $0
+   call $class-implements/F#constructor
+   global.set $class-implements/g
+   block $__inlined_func$class-implements/D#foo@virtual15 (result i32)
+    global.get $~lib/memory/__stack_pointer
+    global.get $class-implements/g
+    local.tee $0
+    i32.store $0
+    i32.const 4
+    local.get $0
+    i32.const 8
+    i32.sub
+    i32.load $0
+    i32.const 10
+    i32.eq
+    br_if $__inlined_func$class-implements/D#foo@virtual15
+    drop
+    i32.const 3
+   end
+   i32.const 4
+   i32.ne
+   if
+    i32.const 0
+    i32.const 1456
+    i32.const 47
+    i32.const 1
+    call $~lib/builtins/abort
+    unreachable
+   end
+   call $class-implements/F#constructor
+   global.set $class-implements/h
+   global.get $~lib/memory/__stack_pointer
+   global.get $class-implements/h
+   local.tee $0
+   i32.store $0
+   block $__inlined_func$class-implements/I#foo@virtual
+    block $default20
+     block $case3
+      block $case2
+       block $case1
+        block $case021
+         local.get $0
+         i32.const 8
+         i32.sub
+         i32.load $0
+         i32.const 3
+         i32.sub
+         br_table $case021 $default20 $case1 $default20 $case2 $default20 $case2 $case3 $default20
+        end
+        i32.const 1
+        local.set $0
+        br $__inlined_func$class-implements/I#foo@virtual
+       end
+       i32.const 2
+       local.set $0
+       br $__inlined_func$class-implements/I#foo@virtual
+      end
+      i32.const 3
+      local.set $0
+      br $__inlined_func$class-implements/I#foo@virtual
+     end
+     i32.const 4
+     local.set $0
+     br $__inlined_func$class-implements/I#foo@virtual
+    end
+    unreachable
+   end
+   local.get $0
+   i32.const 4
+   i32.ne
+   if
+    i32.const 0
+    i32.const 1456
+    i32.const 50
+    i32.const 1
+    call $~lib/builtins/abort
+    unreachable
+   end
    global.get $~lib/memory/__stack_pointer
    i32.const 4
    i32.add
    global.set $~lib/memory/__stack_pointer
    return
   end
-  i32.const 17968
-  i32.const 18016
+  i32.const 18000
+  i32.const 18048
   i32.const 1
   i32.const 1
   call $~lib/builtins/abort
   unreachable
  )
+ (func $class-implements/D#constructor (param $0 i32) (result i32)
+  global.get $~lib/memory/__stack_pointer
+  i32.const 4
+  i32.sub
+  global.set $~lib/memory/__stack_pointer
+  global.get $~lib/memory/__stack_pointer
+  i32.const 1596
+  i32.lt_s
+  if
+   i32.const 18000
+   i32.const 18048
+   i32.const 1
+   i32.const 1
+   call $~lib/builtins/abort
+   unreachable
+  end
+  global.get $~lib/memory/__stack_pointer
+  i32.const 0
+  i32.store $0
+  local.get $0
+  i32.eqz
+  if
+   global.get $~lib/memory/__stack_pointer
+   i32.const 7
+   call $~lib/rt/itcms/__new
+   local.tee $0
+   i32.store $0
+  end
+  global.get $~lib/memory/__stack_pointer
+  i32.const 4
+  i32.add
+  global.set $~lib/memory/__stack_pointer
+  local.get $0
+ )
+ (func $class-implements/F#constructor (result i32)
+  (local $0 i32)
+  global.get $~lib/memory/__stack_pointer
+  i32.const 4
+  i32.sub
+  global.set $~lib/memory/__stack_pointer
+  global.get $~lib/memory/__stack_pointer
+  i32.const 1596
+  i32.lt_s
+  if
+   i32.const 18000
+   i32.const 18048
+   i32.const 1
+   i32.const 1
+   call $~lib/builtins/abort
+   unreachable
+  end
+  global.get $~lib/memory/__stack_pointer
+  local.tee $0
+  i32.const 0
+  i32.store $0
+  local.get $0
+  i32.const 10
+  call $~lib/rt/itcms/__new
+  local.tee $0
+  i32.store $0
+  global.get $~lib/memory/__stack_pointer
+  local.get $0
+  call $class-implements/D#constructor
+  local.tee $0
+  i32.store $0
+  global.get $~lib/memory/__stack_pointer
+  i32.const 4
+  i32.add
+  global.set $~lib/memory/__stack_pointer
+  local.get $0
+ )
  (func $byn-split-outlined-A$~lib/rt/itcms/__visit (param $0 i32)
   (local $1 i32)
   (local $2 i32)
@@ -1465,7 +1748,7 @@
      i32.load $0 offset=8
      i32.eqz
      local.get $1
-     i32.const 17948
+     i32.const 17980
      i32.lt_u
      i32.and
      i32.eqz
diff --git a/tests/compiler/class-implements.ts b/tests/compiler/class-implements.ts
index ec039b7367..cc6bfca763 100644
--- a/tests/compiler/class-implements.ts
+++ b/tests/compiler/class-implements.ts
@@ -2,6 +2,10 @@ interface I {
   foo(): i32;
 }
 
+interface J {
+  foo(): i32;
+}
+
 class A implements I {
   foo(): i32 { return 1; }
 }
@@ -18,3 +22,29 @@ class C extends B implements I {
 
 var c = new C();
 assert(c.foo() == 2);
+
+class D implements I, J {
+  foo(): i32 { return 3; }
+}
+
+let d = new D();
+assert(d.foo() == 3);
+
+class E extends D implements I {
+}
+
+let e = new E();
+assert(e.foo() == 3);
+
+class F extends D implements I {
+  foo(): i32 { return 4; }
+}
+
+let f = new F();
+assert(f.foo() == 4);
+
+let g:D = new F();
+assert(g.foo() == 4);
+
+let h:I = new F();
+assert(h.foo() == 4);