diff --git a/libavformat/avidec.c b/libavformat/avidec.c
index 79000f3e81..547eb63b1b 100644
--- a/libavformat/avidec.c
+++ b/libavformat/avidec.c
@@ -135,7 +135,7 @@ static inline int get_duration(AVIStream *ast, int len)
     if (ast->sample_size)
         return len;
     else if (ast->dshow_block_align)
-        return (len + ast->dshow_block_align - 1) / ast->dshow_block_align;
+        return (len + (int64_t)ast->dshow_block_align - 1) / ast->dshow_block_align;
     else
         return 1;
 }