diff --git a/migration/ram.c b/migration/ram.c
index dc1de9ddbc..1d42414ecc 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -2546,14 +2546,22 @@ static int ram_find_and_save_block(RAMState *rs)
         return pages;
     }
 
+    /*
+     * Always keep last_seen_block/last_page valid during this procedure,
+     * because find_dirty_block() relies on these values (e.g., we compare
+     * last_seen_block with pss.block to see whether we searched all the
+     * ramblocks) to detect the completion of migration.  Having NULL value
+     * of last_seen_block can conditionally cause below loop to run forever.
+     */
+    if (!rs->last_seen_block) {
+        rs->last_seen_block = QLIST_FIRST_RCU(&ram_list.blocks);
+        rs->last_page = 0;
+    }
+
     pss.block = rs->last_seen_block;
     pss.page = rs->last_page;
     pss.complete_round = false;
 
-    if (!pss.block) {
-        pss.block = QLIST_FIRST_RCU(&ram_list.blocks);
-    }
-
     do {
         again = true;
         found = get_queued_page(rs, &pss);