diff --git a/src/nsterm.m b/src/nsterm.m
index 419a37033f7..51a53828b5b 100644
--- a/src/nsterm.m
+++ b/src/nsterm.m
@@ -1946,7 +1946,7 @@ so some key presses (TAB) are swallowed by the system. */
   if (!NILP (new_value)
       && (!FRAMEP (new_value)
 	  || !FRAME_LIVE_P (p = XFRAME (new_value))
-	  || !FRAME_X_P (p)))
+	  || !FRAME_NS_P (p)))
     {
       store_frame_param (f, Qparent_frame, old_value);
       error ("Invalid specification of `parent-frame'");