diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index a37ee45016f680862f83895a66a48aba5faf27ec..d2cb6a877563309e60c8dd95e5280b5bf087f3d6 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -653,6 +653,13 @@ retry:
             goto retry;
         }
     }
+
+    /* Make sure that all offsets in the "allocated" range are representable
+     * in an int64_t */
+    if (s->free_cluster_index - 1 > (INT64_MAX >> s->cluster_bits)) {
+        return -EFBIG;
+    }
+
 #ifdef DEBUG_ALLOC2
     fprintf(stderr, "alloc_clusters: size=%" PRId64 " -> %" PRId64 "\n",
             size,