diff --git a/compileopts/target.go b/compileopts/target.go
index 66bcf714..f36561f9 100644
--- a/compileopts/target.go
+++ b/compileopts/target.go
@@ -100,7 +100,7 @@ func (spec *TargetSpec) overrideProperties(child *TargetSpec) error {
 				}
 			}
 		default:
-			return fmt.Errorf("unknown field type : " + kind.String())
+			return fmt.Errorf("unknown field type: %s", kind)
 		}
 	}
 	return nil