diff -r 64eb02a74f2b dwm.c
--- a/dwm.c	Sat Sep 25 13:39:08 2010 +0000
+++ b/dwm.c	Sun Sep 26 16:18:03 2010 +0200
@@ -1270,7 +1270,7 @@
 		default: break;
 		case XA_WM_TRANSIENT_FOR:
 			if(!c->isfloating && (XGetTransientForHint(dpy, c->win, &trans)) &&
-			   (c->isfloating = (wintoclient(trans))))
+			   (c->isfloating = (wintoclient(trans)) != NULL))
 				arrange(c->mon);
 			break;
 		case XA_WM_NORMAL_HINTS: