diff --git a/libavformat/avidec.c b/libavformat/avidec.c
index 1a9563aed4..efb5d8639e 100644
--- a/libavformat/avidec.c
+++ b/libavformat/avidec.c
@@ -667,7 +667,7 @@ static int avi_read_header(AVFormatContext *s)
             st->start_time = 0;
             avio_rl32(pb); /* buffer size */
             avio_rl32(pb); /* quality */
-            if (ast->cum_len*ast->scale/ast->rate > 3600) {
+            if (ast->cum_len > 3600LL * ast->rate / ast->scale) {
                 av_log(s, AV_LOG_ERROR, "crazy start time, iam scared, giving up\n");
                 ast->cum_len = 0;
             }