Permit omission of a colon before a message-typed map value.
diff --git a/proto/decode.go b/proto/decode.go
index 88622c3..129792e 100644
--- a/proto/decode.go
+++ b/proto/decode.go
@@ -518,9 +518,7 @@
 	if err != nil {
 		return err
 	}
-	sp := new(string)
-	*sp = s
-	*structPointer_String(base, p.field) = sp
+	*structPointer_String(base, p.field) = &s
 	return nil
 }