--- surf.orig/config.def.h	Thu Jan 14 16:31:24 2010
+++ surf/config.def.h	Thu Jan 14 16:30:46 2010
@@ -10,7 +10,7 @@
 
 #define SETPROP(p)       { .v = (char *[]){ "/bin/sh", "-c", \
 	"prop=\"`xprop -id $1 $0 | cut -d '\"' -f 2 | dmenu`\" &&" \
-	"xprop -id $1 -f $0 8s -set $0 \"$prop\"", \
+	"[ -n \"$prop\" ] && xprop -id $1 -f $0 8s -set $0 \"$prop\"", \
 	p, winid, NULL } }
 #define MODKEY GDK_CONTROL_MASK
 static Key keys[] = {