diff --git a/m2ts/vpxpes_parser.cc b/m2ts/vpxpes_parser.cc
index a97a302..764558d 100644
--- a/m2ts/vpxpes_parser.cc
+++ b/m2ts/vpxpes_parser.cc
@@ -35,7 +35,7 @@ bool VpxPesParser::BcmvHeader::Valid() const {
 }
 
 bool VpxPesParser::Open(const std::string& pes_file) {
-  pes_file_size_ = libwebm::GetFileSize(pes_file);
+  pes_file_size_ = static_cast<size_t>(libwebm::GetFileSize(pes_file));
   if (pes_file_size_ <= 0)
     return false;
   pes_file_data_.reserve(static_cast<size_t>(pes_file_size_));