diff --git a/dom/media/mp3/MP3Demuxer.cpp b/dom/media/mp3/MP3Demuxer.cpp
index ccc515afb4..8fbe8da796 100644
--- a/dom/media/mp3/MP3Demuxer.cpp
+++ b/dom/media/mp3/MP3Demuxer.cpp
@@ -676,8 +676,9 @@ MP3TrackDemuxer::Read(uint8_t* aBuffer, int64_t aOffset, int32_t aSize) {
 
   const int64_t streamLen = StreamLength();
   if (mInfo && streamLen > 0) {
+    uint64_t max = streamLen > aOffset ? streamLen - aOffset : 0;
     // Prevent blocking reads after successful initialization.
-    aSize = std::min<int64_t>(aSize, streamLen - aOffset);
+    aSize = std::min<int64_t>(aSize, max);
   }
 
   uint32_t read = 0;