diff --git a/src/parser/deserializer.ts b/src/parser/deserializer.ts
index fde181c5..3806c0b1 100644
--- a/src/parser/deserializer.ts
+++ b/src/parser/deserializer.ts
@@ -173,20 +173,12 @@ function deserializeObject(
         stringSize <= 0 ||
         stringSize > buffer.length - index ||
         buffer[index + stringSize - 1] !== 0
-      )
+      ) {
         throw new Error('bad string length in bson');
-
-      value = buffer.toString('utf8', index, index + stringSize - 1);
-
-      for (let i = 0; i < value.length; i++) {
-        if (value.charCodeAt(i) === 0xfffd) {
-          if (!validateUtf8(buffer, index, index + stringSize - 1)) {
-            throw new Error('Invalid UTF-8 string in BSON document');
-          }
-          break;
-        }
       }
 
+      value = getValidatedString(buffer, index, index + stringSize - 1);
+
       index = index + stringSize;
     } else if (elementType === constants.BSON_DATA_OID) {
       const oid = Buffer.alloc(12);
@@ -464,9 +456,10 @@ function deserializeObject(
         stringSize <= 0 ||
         stringSize > buffer.length - index ||
         buffer[index + stringSize - 1] !== 0
-      )
+      ) {
         throw new Error('bad string length in bson');
-      const symbol = buffer.toString('utf8', index, index + stringSize - 1);
+      }
+      const symbol = getValidatedString(buffer, index, index + stringSize - 1);
       value = promoteValues ? symbol : new BSONSymbol(symbol);
       index = index + stringSize;
     } else if (elementType === constants.BSON_DATA_TIMESTAMP) {
@@ -496,9 +489,10 @@ function deserializeObject(
         stringSize <= 0 ||
         stringSize > buffer.length - index ||
         buffer[index + stringSize - 1] !== 0
-      )
+      ) {
         throw new Error('bad string length in bson');
-      const functionString = buffer.toString('utf8', index, index + stringSize - 1);
+      }
+      const functionString = getValidatedString(buffer, index, index + stringSize - 1);
 
       // If we are evaluating the functions
       if (evalFunctions) {
@@ -538,11 +532,12 @@ function deserializeObject(
         stringSize <= 0 ||
         stringSize > buffer.length - index ||
         buffer[index + stringSize - 1] !== 0
-      )
+      ) {
         throw new Error('bad string length in bson');
+      }
 
       // Javascript function
-      const functionString = buffer.toString('utf8', index, index + stringSize - 1);
+      const functionString = getValidatedString(buffer, index, index + stringSize - 1);
       // Update parse index position
       index = index + stringSize;
       // Parse the element
@@ -670,3 +665,16 @@ function isolateEval(
   // Set the object
   return functionCache[functionString].bind(object);
 }
+
+function getValidatedString(buffer: Buffer, start: number, end: number) {
+  const value = buffer.toString('utf8', start, end);
+  for (let i = 0; i < value.length; i++) {
+    if (value.charCodeAt(i) === 0xfffd) {
+      if (!validateUtf8(buffer, start, end)) {
+        throw new Error('Invalid UTF-8 string in BSON document');
+      }
+      break;
+    }
+  }
+  return value;
+}
diff --git a/test/node/specs/bson-corpus/code.json b/test/node/specs/bson-corpus/code.json
index 6f37349a..b8482b25 100644
--- a/test/node/specs/bson-corpus/code.json
+++ b/test/node/specs/bson-corpus/code.json
@@ -20,48 +20,48 @@
         },
         {
             "description": "two-byte UTF-8 (\u00e9)",
-            "canonical_bson": "190000000261000D000000C3A9C3A9C3A9C3A9C3A9C3A90000",
-            "canonical_extjson": "{\"a\" : \"\\u00e9\\u00e9\\u00e9\\u00e9\\u00e9\\u00e9\"}"
+            "canonical_bson": "190000000D61000D000000C3A9C3A9C3A9C3A9C3A9C3A90000",
+            "canonical_extjson": "{\"a\" : {\"$code\" : \"\\u00e9\\u00e9\\u00e9\\u00e9\\u00e9\\u00e9\"}}"
         },
         {
             "description": "three-byte UTF-8 (\u2606)",
-            "canonical_bson": "190000000261000D000000E29886E29886E29886E298860000",
-            "canonical_extjson": "{\"a\" : \"\\u2606\\u2606\\u2606\\u2606\"}"
+            "canonical_bson": "190000000D61000D000000E29886E29886E29886E298860000",
+            "canonical_extjson": "{\"a\" : {\"$code\" : \"\\u2606\\u2606\\u2606\\u2606\"}}"
         },
         {
             "description": "Embedded nulls",
-            "canonical_bson": "190000000261000D0000006162006261620062616261620000",
-            "canonical_extjson": "{\"a\" : \"ab\\u0000bab\\u0000babab\"}"
+            "canonical_bson": "190000000D61000D0000006162006261620062616261620000",
+            "canonical_extjson": "{\"a\" : {\"$code\" : \"ab\\u0000bab\\u0000babab\"}}"
         }
     ],
     "decodeErrors": [
         {
             "description": "bad code string length: 0 (but no 0x00 either)",
-            "bson": "0C0000000261000000000000"
+            "bson": "0C0000000D61000000000000"
         },
         {
             "description": "bad code string length: -1",
-            "bson": "0C000000026100FFFFFFFF00"
+            "bson": "0C0000000D6100FFFFFFFF00"
         },
         {
             "description": "bad code string length: eats terminator",
-            "bson": "10000000026100050000006200620000"
+            "bson": "100000000D6100050000006200620000"
         },
         {
             "description": "bad code string length: longer than rest of document",
-            "bson": "120000000200FFFFFF00666F6F6261720000"
+            "bson": "120000000D00FFFFFF00666F6F6261720000"
         },
         {
             "description": "code string is not null-terminated",
-            "bson": "1000000002610004000000616263FF00"
+            "bson": "100000000D610004000000616263FF00"
         },
         {
             "description": "empty code string, but extra null",
-            "bson": "0E00000002610001000000000000"
+            "bson": "0E0000000D610001000000000000"
         },
         {
             "description": "invalid UTF-8",
-            "bson": "0E00000002610002000000E90000"
+            "bson": "0E0000000D610002000000E90000"
         }
     ]
 }
diff --git a/test/node/specs/bson-corpus/symbol.json b/test/node/specs/bson-corpus/symbol.json
index 4e46cb95..3dd3577e 100644
--- a/test/node/specs/bson-corpus/symbol.json
+++ b/test/node/specs/bson-corpus/symbol.json
@@ -50,31 +50,31 @@
     "decodeErrors": [
         {
             "description": "bad symbol length: 0 (but no 0x00 either)",
-            "bson": "0C0000000261000000000000"
+            "bson": "0C0000000E61000000000000"
         },
         {
             "description": "bad symbol length: -1",
-            "bson": "0C000000026100FFFFFFFF00"
+            "bson": "0C0000000E6100FFFFFFFF00"
         },
         {
             "description": "bad symbol length: eats terminator",
-            "bson": "10000000026100050000006200620000"
+            "bson": "100000000E6100050000006200620000"
         },
         {
             "description": "bad symbol length: longer than rest of document",
-            "bson": "120000000200FFFFFF00666F6F6261720000"
+            "bson": "120000000E00FFFFFF00666F6F6261720000"
         },
         {
             "description": "symbol is not null-terminated",
-            "bson": "1000000002610004000000616263FF00"
+            "bson": "100000000E610004000000616263FF00"
         },
         {
             "description": "empty symbol, but extra null",
-            "bson": "0E00000002610001000000000000"
+            "bson": "0E0000000E610001000000000000"
         },
         {
             "description": "invalid UTF-8",
-            "bson": "0E00000002610002000000E90000"
+            "bson": "0E0000000E610002000000E90000"
         }
     ]
 }