diff --git a/libavformat/mov.c b/libavformat/mov.c
index 3215b53636..ad0b9a58d3 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -7071,7 +7071,7 @@ static int mov_read_default(MOVContext *c, AVIOContext *pb, MOVAtom atom)
                 c->atom_depth --;
                 return err;
             }
-            if (c->found_moov && c->found_mdat &&
+            if (c->found_moov && c->found_mdat && a.size <= INT64_MAX - start_pos &&
                 ((!(pb->seekable & AVIO_SEEKABLE_NORMAL) || c->fc->flags & AVFMT_FLAG_IGNIDX || c->frag_index.complete) ||
                  start_pos + a.size == avio_size(pb))) {
                 if (!(pb->seekable & AVIO_SEEKABLE_NORMAL) || c->fc->flags & AVFMT_FLAG_IGNIDX || c->frag_index.complete)