diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index e671183522565..aa57b995a6433 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -390,6 +390,7 @@ Bug Fixes to C++ Support
 - Clang no longer crashes when trying to unify the types of arrays with
   certain differences in qualifiers (this could happen during template argument
   deduction or when building a ternary operator). (#GH97005)
+- Fixed type alias CTAD issues involving default template arguments. (#GH134471)
 - The initialization kind of elements of structured bindings
   direct-list-initialized from an array is corrected to direct-initialization.
 - Clang no longer crashes when a coroutine is declared ``[[noreturn]]``. (#GH127327)
diff --git a/clang/lib/Sema/SemaTemplateDeductionGuide.cpp b/clang/lib/Sema/SemaTemplateDeductionGuide.cpp
index b4863cefc3fb4..29c5736a9bf9e 100644
--- a/clang/lib/Sema/SemaTemplateDeductionGuide.cpp
+++ b/clang/lib/Sema/SemaTemplateDeductionGuide.cpp
@@ -690,6 +690,26 @@ SmallVector<unsigned> TemplateParamsReferencedInTemplateArgumentList(
   SemaRef.MarkUsedTemplateParameters(
       DeducedArgs, TemplateParamsList->getDepth(), ReferencedTemplateParams);
 
+  auto MarkDefaultArgs = [&](auto *Param) {
+    if (!Param->hasDefaultArgument())
+      return;
+    SemaRef.MarkUsedTemplateParameters(
+        Param->getDefaultArgument().getArgument(),
+        TemplateParamsList->getDepth(), ReferencedTemplateParams);
+  };
+
+  for (unsigned Index = 0; Index < TemplateParamsList->size(); ++Index) {
+    if (!ReferencedTemplateParams[Index])
+      continue;
+    auto *Param = TemplateParamsList->getParam(Index);
+    if (auto *TTPD = dyn_cast<TemplateTypeParmDecl>(Param))
+      MarkDefaultArgs(TTPD);
+    else if (auto *NTTPD = dyn_cast<NonTypeTemplateParmDecl>(Param))
+      MarkDefaultArgs(NTTPD);
+    else
+      MarkDefaultArgs(cast<TemplateTemplateParmDecl>(Param));
+  }
+
   SmallVector<unsigned> Results;
   for (unsigned Index = 0; Index < TemplateParamsList->size(); ++Index) {
     if (ReferencedTemplateParams[Index])
diff --git a/clang/test/SemaTemplate/deduction-guide.cpp b/clang/test/SemaTemplate/deduction-guide.cpp
index 6db132ca37c7e..066c917537947 100644
--- a/clang/test/SemaTemplate/deduction-guide.cpp
+++ b/clang/test/SemaTemplate/deduction-guide.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -std=c++2a -verify -ast-dump -ast-dump-decl-types -ast-dump-filter "deduction guide" %s | FileCheck %s --strict-whitespace
+// RUN: %clang_cc1 -std=c++2a -verify -ast-dump -ast-dump-decl-types -ast-dump-filter "deduction guide" %s | FileCheck %s --strict-whitespace -dump-input=always
 
 template<auto ...> struct X {};
 template<template<typename X, X> typename> struct Y {};
@@ -771,3 +771,118 @@ D d(24);
 // CHECK-NEXT:  `-ParmVarDecl {{.+}} 'U'
 
 } // namespace GH132616_DeductionGuide
+
+namespace GH133132 {
+
+template <class _Ty>
+struct A {};
+
+template <class T = int, class U = T>
+using AA = A<U>;
+
+AA a{};
+
+// CHECK-LABEL: Dumping GH133132::<deduction guide for AA>:
+// CHECK-NEXT:  FunctionTemplateDecl {{.+}} implicit <deduction guide for AA>
+// CHECK-NEXT:  |-TemplateTypeParmDecl {{.+}} class depth 0 index 0 T
+// CHECK-NEXT:  | `-TemplateArgument type 'int'
+// CHECK-NEXT:  |   `-BuiltinType {{.+}} 'int'
+// CHECK-NEXT:  |-TemplateTypeParmDecl {{.+}} class depth 0 index 1 U
+// CHECK-NEXT:  | `-TemplateArgument type 'T':'type-parameter-0-0'
+// CHECK-NEXT:  |   `-TemplateTypeParmType {{.+}} 'T' dependent depth 0 index 0
+// CHECK-NEXT:  |     `-TemplateTypeParm {{.+}} 'T'
+// CHECK-NEXT:  |-TypeTraitExpr {{.+}} 'bool' __is_deducible
+// CHECK-NEXT:  | |-DeducedTemplateSpecializationType {{.+}} 'GH133132::AA' dependent
+// CHECK-NEXT:  | | `-name: 'GH133132::AA'
+// CHECK-NEXT:  | |   `-TypeAliasTemplateDecl {{.+}} AA
+// CHECK-NEXT:  | `-TemplateSpecializationType {{.+}} 'A<U>' dependent
+// CHECK-NEXT:  |   |-name: 'A':'GH133132::A' qualified
+// CHECK-NEXT:  |   | `-ClassTemplateDecl {{.+}} A
+// CHECK-NEXT:  |   `-TemplateArgument type 'U':'type-parameter-0-1'
+// CHECK-NEXT:  |     `-SubstTemplateTypeParmType {{.+}} 'U' sugar dependent class depth 0 index 0 _Ty
+// CHECK-NEXT:  |       |-FunctionTemplate {{.+}} '<deduction guide for A>'
+// CHECK-NEXT:  |       `-TemplateTypeParmType {{.+}} 'U' dependent depth 0 index 1
+// CHECK-NEXT:  |         `-TemplateTypeParm {{.+}} 'U'
+// CHECK-NEXT:  |-CXXDeductionGuideDecl {{.+}} implicit <deduction guide for AA> 'auto () -> A<U>'
+// CHECK-NEXT:  `-CXXDeductionGuideDecl {{.+}} implicit used <deduction guide for AA> 'auto () -> A<int>' implicit_instantiation
+// CHECK-NEXT:    |-TemplateArgument type 'int'
+// CHECK-NEXT:    | `-BuiltinType {{.+}} 'int'
+// CHECK-NEXT:    `-TemplateArgument type 'int'
+// CHECK-NEXT:      `-BuiltinType {{.+}} 'int'
+
+template <template <class> class _X>
+struct B {};
+
+template <template <class> class _X = A, template <class> class _Y = _X>
+using BB = B<_Y>;
+
+BB b{};
+
+// CHECK-LABEL: Dumping GH133132::<deduction guide for BB>:
+// CHECK-NEXT:  FunctionTemplateDecl {{.+}} implicit <deduction guide for BB>
+// CHECK-NEXT:  |-TemplateTemplateParmDecl {{.+}} depth 0 index 0 _X
+// CHECK-NEXT:  | |-TemplateTypeParmDecl {{.+}} class depth 0 index 0
+// CHECK-NEXT:  | `-TemplateArgument {{.+}} template 'A':'GH133132::A' qualified
+// CHECK-NEXT:  |   `-ClassTemplateDecl {{.+}} A
+// CHECK-NEXT:  |-TemplateTemplateParmDecl {{.+}} depth 0 index 1 _Y
+// CHECK-NEXT:  | |-TemplateTypeParmDecl {{.+}} class depth 0 index 0
+// CHECK-NEXT:  | `-TemplateArgument {{.+}} template '_X':'template-parameter-0-0' qualified
+// CHECK-NEXT:  |   `-TemplateTemplateParmDecl {{.+}} depth 0 index 0 _X
+// CHECK-NEXT:  |-TypeTraitExpr {{.+}} 'bool' __is_deducible
+// CHECK-NEXT:  | |-DeducedTemplateSpecializationType {{.+}} 'GH133132::BB' dependent
+// CHECK-NEXT:  | | `-name: 'GH133132::BB'
+// CHECK-NEXT:  | |   `-TypeAliasTemplateDecl {{.+}} BB
+// CHECK-NEXT:  | `-TemplateSpecializationType {{.+}} 'B<_Y>' dependent
+// CHECK-NEXT:  |   |-name: 'B':'GH133132::B' qualified
+// CHECK-NEXT:  |   | `-ClassTemplateDecl {{.+}} B
+// CHECK-NEXT:  |   `-TemplateArgument template '_Y':'template-parameter-0-1' subst index 0
+// CHECK-NEXT:  |     |-parameter: TemplateTemplateParmDecl {{.+}} depth 0 index 0 _X
+// CHECK-NEXT:  |     |-associated FunctionTemplate {{.+}} '<deduction guide for B>'
+// CHECK-NEXT:  |     `-replacement: '_Y':'template-parameter-0-1' qualified
+// CHECK-NEXT:  |       `-TemplateTemplateParmDecl {{.+}} depth 0 index 1 _Y
+// CHECK-NEXT:  |-CXXDeductionGuideDecl {{.+}} implicit <deduction guide for BB> 'auto () -> B<_Y>'
+// CHECK-NEXT:  `-CXXDeductionGuideDecl {{.+}} implicit used <deduction guide for BB> 'auto () -> B<GH133132::A>' implicit_instantiation
+// CHECK-NEXT:    |-TemplateArgument template 'GH133132::A'
+// CHECK-NEXT:    | `-ClassTemplateDecl {{.+}} A
+// CHECK-NEXT:    `-TemplateArgument template 'GH133132::A'
+// CHECK-NEXT:      `-ClassTemplateDecl {{.+}} A
+
+template <int N = 42, class U = A<decltype(N)>>
+using CC = A<U>;
+
+CC c{};
+
+// CHECK-LABEL: Dumping GH133132::<deduction guide for CC>:
+// CHECK-NEXT:  FunctionTemplateDecl {{.+}} implicit <deduction guide for CC>
+// CHECK-NEXT:  |-NonTypeTemplateParmDecl {{.+}} 'int' depth 0 index 0 N
+// CHECK-NEXT:  | `-TemplateArgument {{.+}} expr '42'
+// CHECK-NEXT:  |   `-IntegerLiteral {{.+}} 'int' 42
+// CHECK-NEXT:  |-TemplateTypeParmDecl {{.+}} class depth 0 index 1 U
+// CHECK-NEXT:  | `-TemplateArgument type 'A<decltype(N)>'
+// CHECK-NEXT:  |   `-ElaboratedType {{.+}} 'A<decltype(N)>' sugar dependent
+// CHECK-NEXT:  |     `-TemplateSpecializationType {{.+}} 'A<decltype(N)>' dependent
+// CHECK-NEXT:  |       |-name: 'A':'GH133132::A' qualified
+// CHECK-NEXT:  |       | `-ClassTemplateDecl {{.+}} A
+// CHECK-NEXT:  |       `-TemplateArgument type 'decltype(N)'
+// CHECK-NEXT:  |         `-DecltypeType {{.+}} 'decltype(N)' dependent
+// CHECK-NEXT:  |           `-DeclRefExpr {{.+}} 'int' NonTypeTemplateParm {{.+}} 'N' 'int'
+// CHECK-NEXT:  |-TypeTraitExpr {{.+}} 'bool' __is_deducible
+// CHECK-NEXT:  | |-DeducedTemplateSpecializationType {{.+}} 'GH133132::CC' dependent
+// CHECK-NEXT:  | | `-name: 'GH133132::CC'
+// CHECK-NEXT:  | |   `-TypeAliasTemplateDecl {{.+}} CC
+// CHECK-NEXT:  | `-TemplateSpecializationType {{.+}} 'A<U>' dependent
+// CHECK-NEXT:  |   |-name: 'A':'GH133132::A' qualified
+// CHECK-NEXT:  |   | `-ClassTemplateDecl {{.+}} A
+// CHECK-NEXT:  |   `-TemplateArgument type 'U':'type-parameter-0-1'
+// CHECK-NEXT:  |     `-SubstTemplateTypeParmType {{.+}} 'U' sugar dependent class depth 0 index 0 _Ty
+// CHECK-NEXT:  |       |-FunctionTemplate {{.+}} '<deduction guide for A>'
+// CHECK-NEXT:  |       `-TemplateTypeParmType {{.+}} 'U' dependent depth 0 index 1
+// CHECK-NEXT:  |         `-TemplateTypeParm {{.+}} 'U'
+// CHECK-NEXT:  |-CXXDeductionGuideDecl {{.+}} implicit <deduction guide for CC> 'auto () -> A<U>'
+// CHECK-NEXT:  `-CXXDeductionGuideDecl {{.+}} implicit used <deduction guide for CC> 'auto () -> A<GH133132::A<int>>' implicit_instantiation
+// CHECK-NEXT:    |-TemplateArgument integral '42'
+// CHECK-NEXT:    `-TemplateArgument type 'GH133132::A<int>'
+// CHECK-NEXT:      `-RecordType {{.+}} 'GH133132::A<int>'
+// CHECK-NEXT:        `-ClassTemplateSpecialization {{.+}} 'A'
+
+}