Index: sys/kern/kern_shutdown.c
===================================================================
--- sys/kern/kern_shutdown.c
+++ sys/kern/kern_shutdown.c
@@ -675,6 +675,10 @@
 	static char buf[256];
 	va_list ap;
 
+	/* If we already panic'd, don't create a double-fault. */
+	if (panicstr != NULL)
+		return;
+
 	va_start(ap, fmt);
 	(void)vsnprintf(buf, sizeof(buf), fmt, ap);
 	va_end(ap);