diff --git a/third_party/libmkv/EbmlBufferWriter.c b/third_party/libmkv/EbmlBufferWriter.c
index 574e4789981046a9b7909b3098becb33e77f0de6..116cbc4e7a93181bcecb46f919d4ccb88d668ad3 100644
--- a/third_party/libmkv/EbmlBufferWriter.c
+++ b/third_party/libmkv/EbmlBufferWriter.c
@@ -18,8 +18,6 @@ void Ebml_Write(EbmlGlobal *glob, const void *buffer_in, unsigned long len) {
 static void _Serialize(EbmlGlobal *glob, const unsigned char *p, const unsigned char *q) {
   while (q != p) {
     --q;
-
-    unsigned long cbWritten;
     memcpy(&(glob->buf[glob->offset]), q, 1);
     glob->offset++;
   }