diff --git a/test/gtest-extra.cc b/test/gtest-extra.cc
index 68f67565..5766cb14 100644
--- a/test/gtest-extra.cc
+++ b/test/gtest-extra.cc
@@ -102,9 +102,19 @@ void File::close() {
     fmt::ThrowSystemError(errno, "cannot close file");
 }
 
+#ifdef _WIN32
+// On Windows the count argument to read and write is unsigned, so convert
+// it from size_t preventing integer overflow.
+inline unsigned ConvertRWCount(std::size_t count) {
+  return count <= UINT_MAX ? count : UINT_MAX;
+}
+#else
+inline std::size_t ConvertRWCount(std::size_t count) { return count; }
+#endif
+
 std::streamsize File::read(void *buffer, std::size_t count) {
   std::streamsize result = 0;
-  FMT_RETRY(result, ::FMT_POSIX(read(fd_, buffer, count)));
+  FMT_RETRY(result, ::FMT_POSIX(read(fd_, buffer, ConvertRWCount(count))));
   if (result == -1)
     fmt::ThrowSystemError(errno, "cannot read from file");
   return result;