diff --git a/refactor/rename/rename_test.go b/refactor/rename/rename_test.go
index 04931a98..1722f7cd 100644
--- a/refactor/rename/rename_test.go
+++ b/refactor/rename/rename_test.go
@@ -1130,6 +1130,9 @@ func TestDiff(t *testing.T) {
 	if runtime.GOOS == "windows" {
 		t.Skipf("diff tool non-existent for windows on builders")
 	}
+	if runtime.GOOS == "plan9" {
+		t.Skipf("plan9 diff tool doesn't support -u flag")
+	}
 
 	defer func() {
 		Diff = false