--- source3/passdb/lookup_sid.c.ORIG	2021-01-26 16:25:59.235435000 +0100
+++ source3/passdb/lookup_sid.c	2021-01-27 13:54:44.541256000 +0100
@@ -1247,7 +1247,7 @@
 {
 	struct wbcDomainSid *wbc_sids = NULL;
 	struct wbcUnixId *wbc_ids = NULL;
-	uint32_t i, num_not_cached;
+	uint32_t i, num_not_cached, num_not_cached_size;
 	wbcErr err;
 	bool ret = false;
 
@@ -1277,7 +1277,8 @@
 		if (idmap_cache_find_sid2unixid(&sids[i], &ids[i], &expired)
 		    && !expired)
 		{
-			continue;
+		  	if (ids[i].type != ID_TYPE_NOT_SPECIFIED)
+			  	continue;
 		}
 		ids[i].type = ID_TYPE_NOT_SPECIFIED;
 		memcpy(&wbc_sids[num_not_cached], &sids[i],
@@ -1300,10 +1301,16 @@
 			   wbcErrorString(err)));
 	}
 
+	num_not_cached_size = num_not_cached;
 	num_not_cached = 0;
 
 	for (i=0; i<num_sids; i++) {
 		if (ids[i].type == ID_TYPE_NOT_SPECIFIED) {
+		  	if (num_not_cached >= num_not_cached_size) {
+			  	DEBUG(0, ("Internal Error: num_not_cached(%d) >= num_not_cached_size(%d), i=%d, num_sids=%d\n",
+					  num_not_cached, num_not_cached_size, i, num_sids));
+				goto fail;
+			}
 			switch (wbc_ids[num_not_cached].type) {
 			case WBC_ID_TYPE_UID:
 				ids[i].type = ID_TYPE_UID;