diff --git a/testing/protocmp/util_test.go b/testing/protocmp/util_test.go
index f9da7e5..6f41ba4 100644
--- a/testing/protocmp/util_test.go
+++ b/testing/protocmp/util_test.go
@@ -145,6 +145,65 @@
 		want: true,
 	}}...)
 
+	// Test message values.
+	tests = append(tests, []test{{
+		x:    testpb.TestAllTypes{OptionalSint64: proto.Int64(1)},
+		y:    testpb.TestAllTypes{OptionalSint64: proto.Int64(1)},
+		opts: cmp.Options{Transform()},
+		want: true,
+	}, {
+		x:    testpb.TestAllTypes{OptionalSint64: proto.Int64(1)},
+		y:    testpb.TestAllTypes{OptionalSint64: proto.Int64(2)},
+		opts: cmp.Options{Transform()},
+		want: false,
+	}, {
+		x:    struct{ M testpb.TestAllTypes }{M: testpb.TestAllTypes{OptionalSint64: proto.Int64(1)}},
+		y:    struct{ M testpb.TestAllTypes }{M: testpb.TestAllTypes{OptionalSint64: proto.Int64(1)}},
+		opts: cmp.Options{Transform()},
+		want: true,
+	}, {
+		x:    struct{ M testpb.TestAllTypes }{M: testpb.TestAllTypes{OptionalSint64: proto.Int64(1)}},
+		y:    struct{ M testpb.TestAllTypes }{M: testpb.TestAllTypes{OptionalSint64: proto.Int64(2)}},
+		opts: cmp.Options{Transform()},
+		want: false,
+	}, {
+		x:    struct{ M []testpb.TestAllTypes }{M: []testpb.TestAllTypes{{OptionalSint64: proto.Int64(1)}}},
+		y:    struct{ M []testpb.TestAllTypes }{M: []testpb.TestAllTypes{{OptionalSint64: proto.Int64(1)}}},
+		opts: cmp.Options{Transform()},
+		want: true,
+	}, {
+		x:    struct{ M []testpb.TestAllTypes }{M: []testpb.TestAllTypes{{OptionalSint64: proto.Int64(1)}}},
+		y:    struct{ M []testpb.TestAllTypes }{M: []testpb.TestAllTypes{{OptionalSint64: proto.Int64(2)}}},
+		opts: cmp.Options{Transform()},
+		want: false,
+	}, {
+		x: struct {
+			M map[string]testpb.TestAllTypes
+		}{
+			M: map[string]testpb.TestAllTypes{"k": {OptionalSint64: proto.Int64(1)}},
+		},
+		y: struct {
+			M map[string]testpb.TestAllTypes
+		}{
+			M: map[string]testpb.TestAllTypes{"k": {OptionalSint64: proto.Int64(1)}},
+		},
+		opts: cmp.Options{Transform()},
+		want: true,
+	}, {
+		x: struct {
+			M map[string]testpb.TestAllTypes
+		}{
+			M: map[string]testpb.TestAllTypes{"k": {OptionalSint64: proto.Int64(1)}},
+		},
+		y: struct {
+			M map[string]testpb.TestAllTypes
+		}{
+			M: map[string]testpb.TestAllTypes{"k": {OptionalSint64: proto.Int64(2)}},
+		},
+		opts: cmp.Options{Transform()},
+		want: false,
+	}}...)
+
 	// Test IgnoreUnknown.
 	raw := pack.Message{
 		pack.Tag{1, pack.BytesType}, pack.String("Hello, goodbye!"),
diff --git a/testing/protocmp/xform.go b/testing/protocmp/xform.go
index e27c890..a42bf9b 100644
--- a/testing/protocmp/xform.go
+++ b/testing/protocmp/xform.go
@@ -161,10 +161,18 @@
 	// NOTE: There are currently no custom options for Transform,
 	// but the use of an unexported type keeps the future open.
 
+	// addrType returns a pointer to t if t isn't a pointer or interface.
+	addrType := func(t reflect.Type) reflect.Type {
+		if k := t.Kind(); k == reflect.Interface || k == reflect.Ptr {
+			return t
+		}
+		return reflect.PtrTo(t)
+	}
+
 	// TODO: Should this transform protoreflect.Enum types to Enum as well?
 	return cmp.FilterPath(func(p cmp.Path) bool {
 		ps := p.Last()
-		if isMessageType(ps.Type()) {
+		if isMessageType(addrType(ps.Type())) {
 			return true
 		}
 
@@ -175,11 +183,19 @@
 			if !vx.IsValid() || vx.IsNil() || !vy.IsValid() || vy.IsNil() {
 				return false
 			}
-			return isMessageType(vx.Elem().Type()) && isMessageType(vy.Elem().Type())
+			return isMessageType(addrType(vx.Elem().Type())) && isMessageType(addrType(vy.Elem().Type()))
 		}
 
 		return false
 	}, cmp.Transformer("protocmp.Transform", func(v interface{}) Message {
+		// For user convenience, shallow copy the message value if necessary
+		// in order for it to implement the message interface.
+		if rv := reflect.ValueOf(v); rv.IsValid() && rv.Kind() != reflect.Ptr && !isMessageType(rv.Type()) {
+			pv := reflect.New(rv.Type())
+			pv.Elem().Set(rv)
+			v = pv.Interface()
+		}
+
 		m := protoimpl.X.MessageOf(v)
 		switch {
 		case m == nil: