diff --git a/migration/block-dirty-bitmap.c b/migration/block-dirty-bitmap.c
index 35f5ef688d..9aba7d9c22 100644
--- a/migration/block-dirty-bitmap.c
+++ b/migration/block-dirty-bitmap.c
@@ -1215,7 +1215,10 @@ static int dirty_bitmap_save_setup(QEMUFile *f, void *opaque)
 {
     DBMSaveState *s = &((DBMState *)opaque)->save;
     SaveBitmapState *dbms = NULL;
+
+    qemu_mutex_lock_iothread();
     if (init_dirty_bitmap_migration(s) < 0) {
+        qemu_mutex_unlock_iothread();
         return -1;
     }
 
@@ -1223,7 +1226,7 @@ static int dirty_bitmap_save_setup(QEMUFile *f, void *opaque)
         send_bitmap_start(f, s, dbms);
     }
     qemu_put_bitmap_flags(f, DIRTY_BITMAP_MIG_FLAG_EOS);
-
+    qemu_mutex_unlock_iothread();
     return 0;
 }