diff --git a/src/google/protobuf/descriptor_unittest.cc b/src/google/protobuf/descriptor_unittest.cc
index f0a9dc69c1..eb7e4e77c2 100644
--- a/src/google/protobuf/descriptor_unittest.cc
+++ b/src/google/protobuf/descriptor_unittest.cc
@@ -34,6 +34,7 @@
 //
 // This file makes extensive use of RFC 3092.  :)
 
+#include <cstdlib>
 #include <limits>
 #include <memory>
 #include <vector>