diff --git a/util/autovector_test.cc b/util/autovector_test.cc
index 6d709a374..eb244aabf 100644
--- a/util/autovector_test.cc
+++ b/util/autovector_test.cc
@@ -17,7 +17,7 @@ using namespace std;
 
 class AutoVectorTest { };
 
-const size_t kSize = 8;
+const unsigned long kSize = 8;
 TEST(AutoVectorTest, PushBackAndPopBack) {
   autovector<size_t, kSize> vec;
   ASSERT_TRUE(vec.empty());