Index: sys/dev/ofw/openfirm.c
===================================================================
--- sys/dev/ofw/openfirm.c
+++ sys/dev/ofw/openfirm.c
@@ -394,6 +394,9 @@
 	KASSERT(len % 4 == 0, ("Need a multiple of 4 bytes"));
 
 	retval = OF_getprop(node, propname, buf, len);
+	if (retval <= 0)
+		return (retval);
+
 	for (i = 0; i < len/4; i++)
 		buf[i] = be32toh(buf[i]);