diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index ef965d7895..0d64bf5a5e 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -3455,6 +3455,8 @@ int qcow2_detect_metadata_preallocation(BlockDriverState *bs)
     int64_t i, end_cluster, cluster_count = 0, threshold;
     int64_t file_length, real_allocation, real_clusters;
 
+    qemu_co_mutex_assert_locked(&s->lock);
+
     file_length = bdrv_getlength(bs->file->bs);
     if (file_length < 0) {
         return file_length;
diff --git a/block/qcow2.c b/block/qcow2.c
index 8b05933565..0bc69e6996 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1916,6 +1916,8 @@ static int coroutine_fn qcow2_co_block_status(BlockDriverState *bs,
     unsigned int bytes;
     int status = 0;
 
+    qemu_co_mutex_lock(&s->lock);
+
     if (!s->metadata_preallocation_checked) {
         ret = qcow2_detect_metadata_preallocation(bs);
         s->metadata_preallocation = (ret == 1);
@@ -1923,7 +1925,6 @@ static int coroutine_fn qcow2_co_block_status(BlockDriverState *bs,
     }
 
     bytes = MIN(INT_MAX, count);
-    qemu_co_mutex_lock(&s->lock);
     ret = qcow2_get_cluster_offset(bs, offset, &bytes, &cluster_offset);
     qemu_co_mutex_unlock(&s->lock);
     if (ret < 0) {