diff --git a/proto/decode.go b/proto/decode.go
index 3c58cfb..59189d7 100644
--- a/proto/decode.go
+++ b/proto/decode.go
@@ -441,7 +441,7 @@
 			// Not enough information to determine the exact field. If we use extra
 			// CPU, we could determine the field only if the missing required field
 			// has a tag <= 64 and we check reqFields.
-			return &ErrRequiredNotSet{"{Unknown}"}
+			return &RequiredNotSetError{"{Unknown}"}
 		}
 	}
 	return err