diff --git a/libavformat/xwma.c b/libavformat/xwma.c
index b77c6ed605..d2333feb93 100644
--- a/libavformat/xwma.c
+++ b/libavformat/xwma.c
@@ -269,7 +269,7 @@ static int xwma_read_header(AVFormatContext *s)
              * an offset / timestamp pair.
              */
             av_add_index_entry(st,
-                               cur_pos + (i+1) * st->codecpar->block_align, /* pos */
+                               cur_pos + (i+1LL) * st->codecpar->block_align, /* pos */
                                dpds_table[i] / bytes_per_sample,            /* timestamp */
                                st->codecpar->block_align,                   /* size */
                                0,                                           /* duration */