diff --git a/objectivec/GPBMessage.h b/objectivec/GPBMessage.h
index 896a4c6577db..5b7ce0cb4a49 100644
--- a/objectivec/GPBMessage.h
+++ b/objectivec/GPBMessage.h
@@ -410,6 +410,12 @@ CF_EXTERN_C_END
  * repeated fields. If the extension is a Message one will be auto created for
  * you and returned similar to fields.
  *
+ * NOTE: For Enum extensions, if the enum was _closed_, then unknown values
+ * were parsed into the message's unknown fields instead of ending up in the
+ * extensions, just like what happens with singular/repeated fields. For open
+ * enums, the _raw_ value will be in the NSNumber, meaning if one does a
+ * `switch` on the values, a `default` case should also be included.
+ *
  * @param extension The extension descriptor of the extension to fetch.
  *
  * @return The extension matching the given descriptor, or nil if none found.
diff --git a/objectivec/GPBMessage.m b/objectivec/GPBMessage.m
index b2d5b79a66a1..334217919c1e 100644
--- a/objectivec/GPBMessage.m
+++ b/objectivec/GPBMessage.m
@@ -108,6 +108,7 @@ static id CreateMapForField(GPBFieldDescriptor *field, GPBMessage *autocreator)
 static id GetMapIvarWithField(GPBMessage *self, GPBFieldDescriptor *field);
 static NSMutableDictionary *CloneExtensionMap(NSDictionary *extensionMap, NSZone *zone)
     __attribute__((ns_returns_retained));
+static GPBUnknownFieldSet *GetOrMakeUnknownFields(GPBMessage *self);
 
 #ifdef DEBUG
 static NSError *MessageError(NSInteger code, NSDictionary *userInfo) {
@@ -638,6 +639,7 @@ static id GetMapIvarWithField(GPBMessage *self, GPBFieldDescriptor *field) {
 #endif  // !defined(__clang_analyzer__)
 
 static id NewSingleValueFromInputStream(GPBExtensionDescriptor *extension,
+                                        GPBMessage *messageToGetExtension,
                                         GPBCodedInputStream *input,
                                         id<GPBExtensionRegistry> extensionRegistry,
                                         GPBMessage *existingValue)
@@ -645,6 +647,7 @@ static id NewSingleValueFromInputStream(GPBExtensionDescriptor *extension,
 
 // Note that this returns a retained value intentionally.
 static id NewSingleValueFromInputStream(GPBExtensionDescriptor *extension,
+                                        GPBMessage *messageToGetExtension,
                                         GPBCodedInputStream *input,
                                         id<GPBExtensionRegistry> extensionRegistry,
                                         GPBMessage *existingValue) {
@@ -681,8 +684,20 @@ static id NewSingleValueFromInputStream(GPBExtensionDescriptor *extension,
       return GPBCodedInputStreamReadRetainedBytes(state);
     case GPBDataTypeString:
       return GPBCodedInputStreamReadRetainedString(state);
-    case GPBDataTypeEnum:
-      return [[NSNumber alloc] initWithInt:GPBCodedInputStreamReadEnum(state)];
+    case GPBDataTypeEnum: {
+      int32_t val = GPBCodedInputStreamReadEnum(&input->state_);
+      GPBEnumDescriptor *enumDescriptor = extension.enumDescriptor;
+      // If run with source generated before the closed enum support, all enums
+      // will be considers not closed, so casing to the enum type for a switch
+      // could cause things to fall off the end of a switch.
+      if (!enumDescriptor.isClosed || enumDescriptor.enumVerifier(val)) {
+        return [[NSNumber alloc] initWithInt:val];
+      } else {
+        GPBUnknownFieldSet *unknownFields = GetOrMakeUnknownFields(messageToGetExtension);
+        [unknownFields mergeVarintField:extension->description_->fieldNumber value:val];
+        return nil;
+      }
+    }
     case GPBDataTypeGroup:
     case GPBDataTypeMessage: {
       GPBMessage *message;
@@ -726,9 +741,11 @@ static void ExtensionMergeFromInputStream(GPBExtensionDescriptor *extension, BOO
     int32_t length = GPBCodedInputStreamReadInt32(state);
     size_t limit = GPBCodedInputStreamPushLimit(state, length);
     while (GPBCodedInputStreamBytesUntilLimit(state) > 0) {
-      id value = NewSingleValueFromInputStream(extension, input, extensionRegistry, nil);
-      [message addExtension:extension value:value];
-      [value release];
+      id value = NewSingleValueFromInputStream(extension, message, input, extensionRegistry, nil);
+      if (value) {
+        [message addExtension:extension value:value];
+        [value release];
+      }
     }
     GPBCodedInputStreamPopLimit(state, limit);
   } else {
@@ -737,13 +754,16 @@ static void ExtensionMergeFromInputStream(GPBExtensionDescriptor *extension, BOO
     if (!isRepeated && GPBDataTypeIsMessage(description->dataType)) {
       existingValue = [message getExistingExtension:extension];
     }
-    id value = NewSingleValueFromInputStream(extension, input, extensionRegistry, existingValue);
-    if (isRepeated) {
-      [message addExtension:extension value:value];
-    } else {
-      [message setExtension:extension value:value];
+    id value =
+        NewSingleValueFromInputStream(extension, message, input, extensionRegistry, existingValue);
+    if (value) {
+      if (isRepeated) {
+        [message addExtension:extension value:value];
+      } else {
+        [message setExtension:extension value:value];
+      }
+      [value release];
     }
-    [value release];
   }
 }
 
diff --git a/objectivec/Tests/GPBMessageTests.m b/objectivec/Tests/GPBMessageTests.m
index 7d4cf79c3df2..6a1d48beda4b 100644
--- a/objectivec/Tests/GPBMessageTests.m
+++ b/objectivec/Tests/GPBMessageTests.m
@@ -1481,6 +1481,82 @@ - (void)testExtensionsMergeFrom {
   XCTAssertEqualObjects(message, message2);
 }
 
+- (void)testClosedEnumsInExtensions {
+  // Only unknown values.
+
+  NSData *data =
+      DataFromCStr("\xA8\x01\x0A"      // optional_nested_enum_extension set to 10
+                   "\x98\x03\x0B"      // repeated_nested_enum_extension set to 11
+                   "\xA2\x03\x01\x0C"  // repeated_foreign_enum_extension set to 12 (packed)
+      );
+  NSError *error = nil;
+
+  TestAllExtensions *msg = [TestAllExtensions parseFromData:data
+                                          extensionRegistry:[self extensionRegistry]
+                                                      error:&error];
+  XCTAssertNil(error);
+
+  XCTAssertFalse([msg hasExtension:[UnittestRoot optionalNestedEnumExtension]]);
+  XCTAssertFalse([msg hasExtension:[UnittestRoot repeatedNestedEnumExtension]]);
+  XCTAssertFalse([msg hasExtension:[UnittestRoot repeatedForeignEnumExtension]]);
+
+  GPBUnknownFieldSet *unknownFields = msg.unknownFields;
+  GPBUnknownField *field =
+      [unknownFields getField:[UnittestRoot optionalNestedEnumExtension].fieldNumber];
+  XCTAssertNotNil(field);
+  XCTAssertEqual(field.varintList.count, 1);
+  XCTAssertEqual([field.varintList valueAtIndex:0], 10);
+  field = [unknownFields getField:[UnittestRoot repeatedNestedEnumExtension].fieldNumber];
+  XCTAssertNotNil(field);
+  XCTAssertEqual(field.varintList.count, 1);
+  XCTAssertEqual([field.varintList valueAtIndex:0], 11);
+  field = [unknownFields getField:[UnittestRoot repeatedForeignEnumExtension].fieldNumber];
+  XCTAssertNotNil(field);
+  XCTAssertEqual(field.varintList.count, 1);
+  XCTAssertEqual([field.varintList valueAtIndex:0], 12);
+
+  // Unknown and known, the known come though an unknown go to unknown fields.
+
+  data = DataFromCStr(
+      "\xA8\x01\x01"              // optional_nested_enum_extension set to 1
+      "\xA8\x01\x0A"              // optional_nested_enum_extension set to 10
+      "\xA8\x01\x02"              // optional_nested_enum_extension set to 2
+      "\x98\x03\x02"              // repeated_nested_enum_extension set to 2
+      "\x98\x03\x0B"              // repeated_nested_enum_extension set to 11
+      "\x98\x03\x03"              // repeated_nested_enum_extension set to 3
+      "\xA2\x03\x03\x04\x0C\x06"  // repeated_foreign_enum_extension set to 4, 12, 6 (packed)
+  );
+  error = nil;
+
+  msg = [TestAllExtensions parseFromData:data
+                       extensionRegistry:[self extensionRegistry]
+                                   error:&error];
+  XCTAssertNil(error);
+
+  XCTAssertTrue([msg hasExtension:[UnittestRoot optionalNestedEnumExtension]]);
+  XCTAssertEqualObjects([msg getExtension:[UnittestRoot optionalNestedEnumExtension]], @2);
+  XCTAssertTrue([msg hasExtension:[UnittestRoot repeatedNestedEnumExtension]]);
+  id expected = @[ @2, @3 ];
+  XCTAssertEqualObjects([msg getExtension:[UnittestRoot repeatedNestedEnumExtension]], expected);
+  XCTAssertTrue([msg hasExtension:[UnittestRoot repeatedForeignEnumExtension]]);
+  expected = @[ @4, @6 ];
+  XCTAssertEqualObjects([msg getExtension:[UnittestRoot repeatedForeignEnumExtension]], expected);
+
+  unknownFields = msg.unknownFields;
+  field = [unknownFields getField:[UnittestRoot optionalNestedEnumExtension].fieldNumber];
+  XCTAssertNotNil(field);
+  XCTAssertEqual(field.varintList.count, 1);
+  XCTAssertEqual([field.varintList valueAtIndex:0], 10);
+  field = [unknownFields getField:[UnittestRoot repeatedNestedEnumExtension].fieldNumber];
+  XCTAssertNotNil(field);
+  XCTAssertEqual(field.varintList.count, 1);
+  XCTAssertEqual([field.varintList valueAtIndex:0], 11);
+  field = [unknownFields getField:[UnittestRoot repeatedForeignEnumExtension].fieldNumber];
+  XCTAssertNotNil(field);
+  XCTAssertEqual(field.varintList.count, 1);
+  XCTAssertEqual([field.varintList valueAtIndex:0], 12);
+}
+
 - (void)testDefaultingExtensionMessages {
   TestAllExtensions *message = [TestAllExtensions message];