diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
index 784973a951..e1528a9162 100644
--- a/libavformat/matroskaenc.c
+++ b/libavformat/matroskaenc.c
@@ -2451,7 +2451,7 @@ static int mkv_write_trailer(AVFormatContext *s)
         }
     }
 
-    if (mkv->cluster_bc) {
+    if (mkv->cluster_pos != -1) {
         end_ebml_master_crc32(pb, &mkv->cluster_bc, mkv,
                               MATROSKA_ID_CLUSTER, 0, 0);
     }