diff --git a/dmenu.c b/dmenu.c
index 085dc29..19f6385 100644
--- a/dmenu.c
+++ b/dmenu.c
@@ -415,8 +415,9 @@ keypress(XKeyEvent *ev)
 	switch(ksym) {
 	default:
 insert:
-		if (!iscntrl(*buf))
-			insert(buf, len);
+		if (iscntrl((unsigned char)*buf))
+			return;
+		insert(buf, len);
 		break;
 	case XK_Delete:
 	case XK_KP_Delete: