diff --git a/cmd/protoc-gen-go/internal_gengo/main.go b/cmd/protoc-gen-go/internal_gengo/main.go
index 96b27fb..b5b6655 100644
--- a/cmd/protoc-gen-go/internal_gengo/main.go
+++ b/cmd/protoc-gen-go/internal_gengo/main.go
@@ -824,8 +824,8 @@
 	// differently in other languages:
 	// https://github.com/google/protobuf/blob/aff10976/src/google/protobuf/text_format.cc#L1560
 	name := extension.Desc.FullName()
-	if isExtensionMessageSetElement(gen, extension) {
-		name = name.Parent()
+	if n, ok := isExtensionMessageSetElement(extension); ok {
+		name = n
 	}
 
 	g.P("var ", extensionVar(f.File, extension), " = &", protogen.GoIdent{
@@ -846,10 +846,27 @@
 	g.P()
 }
 
-func isExtensionMessageSetElement(gen *protogen.Plugin, extension *protogen.Extension) bool {
-	return extension.ParentMessage != nil &&
-		extension.ExtendedType.Desc.Options().(*descpb.MessageOptions).GetMessageSetWireFormat() &&
-		extension.Desc.Name() == "message_set_extension"
+// isExtensionMessageSetELement returns the adjusted name of an extension
+// which extends proto2.bridge.MessageSet.
+func isExtensionMessageSetElement(extension *protogen.Extension) (name protoreflect.FullName, ok bool) {
+	opts := extension.ExtendedType.Desc.Options().(*descpb.MessageOptions)
+	if !opts.GetMessageSetWireFormat() || extension.Desc.Name() != "message_set_extension" {
+		return "", false
+	}
+	if extension.ParentMessage == nil {
+		// This case shouldn't be given special handling at all--we're
+		// only supposed to drop the ".message_set_extension" for
+		// extensions defined within a message (i.e., the extension
+		// takes the message's name).
+		//
+		// This matches the behavior of the v1 generator, however.
+		//
+		// TODO: See if we can drop this case.
+		name = extension.Desc.FullName()
+		name = name[:len(name)-len("message_set_extension")]
+		return name, true
+	}
+	return extension.Desc.FullName().Parent(), true
 }
 
 // extensionVar returns the var holding the ExtensionDesc for an extension.
@@ -928,7 +945,7 @@
 		GoImportPath: protoPackage,
 		GoName:       "RegisterExtension",
 	}, "(", extensionVar(f.File, extension), ")")
-	if isExtensionMessageSetElement(gen, extension) {
+	if name, ok := isExtensionMessageSetElement(extension); ok {
 		goType, pointer := fieldGoType(g, extension)
 		if pointer {
 			goType = "*" + goType
@@ -936,7 +953,7 @@
 		g.P(protogen.GoIdent{
 			GoImportPath: protoPackage,
 			GoName:       "RegisterMessageSetType",
-		}, "((", goType, ")(nil), ", extension.Desc.Number(), ",", strconv.Quote(string(extension.Desc.FullName().Parent())), ")")
+		}, "((", goType, ")(nil), ", extension.Desc.Number(), ",", strconv.Quote(string(name)), ")")
 	}
 }
 
diff --git a/cmd/protoc-gen-go/testdata/extensions/ext/ext.pb.go b/cmd/protoc-gen-go/testdata/extensions/ext/ext.pb.go
index e205a86..4170822 100644
--- a/cmd/protoc-gen-go/testdata/extensions/ext/ext.pb.go
+++ b/cmd/protoc-gen-go/testdata/extensions/ext/ext.pb.go
@@ -734,6 +734,15 @@
 	Filename:      "extensions/ext/ext.proto",
 }
 
+var E_MessageSetExtension = &proto.ExtensionDesc{
+	ExtendedType:  (*base.MessageSetWireFormatMessage)(nil),
+	ExtensionType: (*MessageSetWireFormatExtension)(nil),
+	Field:         101,
+	Name:          "goproto.protoc.extension.ext.",
+	Tag:           "bytes,101,opt,name=message_set_extension",
+	Filename:      "extensions/ext/ext.proto",
+}
+
 func init() {
 	proto.RegisterEnum("goproto.protoc.extension.ext.Enum", Enum_name, Enum_value)
 	proto.RegisterType((*Message)(nil), "goproto.protoc.extension.ext.Message")
@@ -788,80 +797,82 @@
 	proto.RegisterExtension(E_Repeatedgroup)
 	proto.RegisterExtension(E_ExtendableField)
 	proto.RegisterExtension(E_ExtendableStringField)
+	proto.RegisterExtension(E_MessageSetExtension)
+	proto.RegisterMessageSetType((*MessageSetWireFormatExtension)(nil), 101, "goproto.protoc.extension.ext.")
 }
 
 func init() { proto.RegisterFile("extensions/ext/ext.proto", fileDescriptor_bf470ef4907b23cb) }
 
 var fileDescriptor_bf470ef4907b23cb = []byte{
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+	// 1120 bytes of a gzipped FileDescriptorProto
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+	0xe8, 0x60, 0x79, 0xcf, 0x0c, 0x98, 0x65, 0x0a, 0x1d, 0xcc, 0x10, 0xf9, 0xb2, 0x8d, 0x3f, 0x0d,
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+	0xb6, 0x89, 0xb0, 0x47, 0x7b, 0x4b, 0x98, 0x5d, 0xa4, 0x7d, 0xf9, 0x2b, 0x3a, 0xe6, 0xd4, 0xf5,
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+	0x24, 0xf7, 0x07, 0xca, 0x55, 0x0a, 0x42, 0x2c, 0x81, 0x4b, 0xb8, 0xf4, 0x8f, 0x14, 0x5c, 0x2b,
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+	0x5b, 0x59, 0xce, 0x89, 0x51, 0xdf, 0x87, 0x8a, 0x00, 0x2f, 0xc3, 0xfe, 0x99, 0xb2, 0xb7, 0xf4,
+	0xb4, 0x58, 0xe7, 0x89, 0x55, 0xe7, 0x0b, 0x28, 0xef, 0xd5, 0xbf, 0x50, 0x70, 0x45, 0x28, 0x20,
+	0x37, 0xeb, 0x55, 0x72, 0x48, 0x2a, 0xfd, 0x94, 0x92, 0x9b, 0x4b, 0x72, 0xf0, 0x91, 0xa8, 0x28,
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+	0x0c, 0x84, 0xfe, 0x88, 0x2d, 0xbb, 0xd0, 0xd1, 0xf2, 0x9e, 0xfd, 0x3b, 0x7f, 0xd0, 0x13, 0x3a,
+	0x9a, 0x9b, 0x76, 0xbe, 0x80, 0xf2, 0xae, 0xfd, 0x07, 0xe5, 0x6e, 0x0b, 0x05, 0xe4, 0xb6, 0xbd,
+	0x00, 0x39, 0x91, 0xcb, 0x18, 0xf7, 0x9f, 0x94, 0xbc, 0xb9, 0x73, 0xa7, 0x09, 0x24, 0x96, 0xf1,
+	0x04, 0xa6, 0x77, 0x5d, 0x79, 0xcb, 0xfc, 0x8b, 0x06, 0x87, 0xea, 0x1b, 0xeb, 0x83, 0xe7, 0x9e,
+	0xaf, 0xf5, 0x7c, 0x38, 0x2a, 0x01, 0x1f, 0x27, 0xd8, 0x43, 0xb4, 0x31, 0x71, 0xc8, 0xd4, 0x92,
+	0xca, 0xe1, 0x8b, 0x2a, 0xb3, 0x4d, 0xbc, 0xc9, 0xeb, 0x02, 0x1a, 0x22, 0x9e, 0xc8, 0xd8, 0xf6,
+	0x11, 0x8d, 0xa6, 0x7d, 0x08, 0x5f, 0x11, 0x32, 0xe0, 0x5d, 0x13, 0x27, 0xb2, 0x31, 0xb5, 0xcd,
+	0x5f, 0x90, 0xdc, 0xca, 0x40, 0xbc, 0x73, 0x78, 0x84, 0x17, 0xf3, 0xb8, 0x4f, 0x5e, 0xcc, 0xe3,
+	0xfe, 0xc1, 0xf1, 0x83, 0x7b, 0xb6, 0x13, 0x3e, 0x8c, 0xc6, 0xbd, 0x0b, 0x6f, 0xd6, 0xb7, 0xbd,
+	0xa9, 0xe9, 0xda, 0x7d, 0x06, 0x1f, 0x47, 0x93, 0xfe, 0x23, 0xb5, 0x7f, 0x31, 0xb3, 0xf8, 0xfe,
+	0xc5, 0x5d, 0x9b, 0xb8, 0x77, 0x6d, 0xaf, 0x1f, 0x92, 0x20, 0xb4, 0xcc, 0x90, 0xbd, 0x0e, 0x13,
+	0xde, 0x8f, 0x3d, 0x0b, 0x00, 0x00, 0xff, 0xff, 0xe1, 0x33, 0x5c, 0xd7, 0x84, 0x13, 0x00, 0x00,
 }
diff --git a/cmd/protoc-gen-go/testdata/extensions/ext/ext.proto b/cmd/protoc-gen-go/testdata/extensions/ext/ext.proto
index 0bb263a..9997a84 100644
--- a/cmd/protoc-gen-go/testdata/extensions/ext/ext.proto
+++ b/cmd/protoc-gen-go/testdata/extensions/ext/ext.proto
@@ -101,3 +101,8 @@
     optional MessageSetWireFormatExtension message_set_extension = 100;
   }
 }
+
+// Message set extension, not nested in a message.
+extend goproto.protoc.extension.base.MessageSetWireFormatMessage {
+  optional MessageSetWireFormatExtension message_set_extension = 101;
+}