--- xlock/xlock.c
+++ xlock/xlock.c
@@ -3367,6 +3367,8 @@
 
 #ifdef USE_MB
 	fontset = createFontSet(dsp, fontsetname);
+	if (fontset == NULL)
+	  exit(1);
 	XmbTextExtents(fontset, "Aj", 1, NULL, &mbRect);
 	planfontset = createFontSet(dsp, planfontsetname);
 	XmbTextExtents(planfontset, "Aj", 1, NULL, &planmbRect);