diff --git a/src/encoding/gob/encoder_test.go b/src/encoding/gob/encoder_test.go
index 0ea4c0ec8e..4af7195209 100644
--- a/src/encoding/gob/encoder_test.go
+++ b/src/encoding/gob/encoder_test.go
@@ -951,6 +951,6 @@ func TestErrorForHugeSlice(t *testing.T) {
 		t.Fatal("decode: no error")
 	}
 	if !strings.Contains(err.Error(), "slice too big") {
-		t.Fatal("decode: expected slice too big error, got %s", err.Error())
+		t.Fatalf("decode: expected slice too big error, got %s", err.Error())
 	}
 }