--- a/sys/vfs/hammer/hammer_btree.c
+++ b/sys/vfs/hammer/hammer_btree.c
@@ -727,8 +727,11 @@
 		return(EINVAL);
 	data_off = elm->leaf.data_offset;
 	data_len = elm->leaf.data_len;
-	if (data_off == 0)
-		return(0);
+	if (data_off == 0) {
+		hdkprintf("illegal zero data_offset in leaf key %016jx\n",
+			  (intmax_t)elm->leaf.base.key);
+		return(EINVAL);
+	}
 
 	/*
 	 * Load the data