diff --git a/src/utils.cc b/src/utils.cc
index 1381c82c..bbe9390b 100644
--- a/src/utils.cc
+++ b/src/utils.cc
@@ -450,7 +450,8 @@ void UpdateTestExpectation(const std::string& filename,
   str.replace(it, expectation.size(), actual);
 
   // Write it back out.
-  std::ofstream of(filename, std::ios::out | std::ios::trunc);
+  std::ofstream of(filename,
+                   std::ios::out | std::ios::trunc | std::ios::binary);
   of.write(str.c_str(), str.size());
   of.close();
 }