diff --git a/block/blkdebug.c b/block/blkdebug.c
index 5ccb9cecb3d0c015bf5dc42030711702e227a53d..63bc5d4f0340ecd3c758949dada273e2be6f2fe5 100644
--- a/block/blkdebug.c
+++ b/block/blkdebug.c
@@ -840,9 +840,13 @@ static void blkdebug_refresh_filename(BlockDriverState *bs, QDict *options)
     }
 
     if (!force_json && bs->file->bs->exact_filename[0]) {
-        snprintf(bs->exact_filename, sizeof(bs->exact_filename),
-                 "blkdebug:%s:%s", s->config_file ?: "",
-                 bs->file->bs->exact_filename);
+        int ret = snprintf(bs->exact_filename, sizeof(bs->exact_filename),
+                           "blkdebug:%s:%s", s->config_file ?: "",
+                           bs->file->bs->exact_filename);
+        if (ret >= sizeof(bs->exact_filename)) {
+            /* An overflow makes the filename unusable, so do not report any */
+            bs->exact_filename[0] = 0;
+        }
     }
 
     opts = qdict_new();