diff --git a/re2/testing/dfa_test.cc b/re2/testing/dfa_test.cc
index 09d31f8..9430bbc 100644
--- a/re2/testing/dfa_test.cc
+++ b/re2/testing/dfa_test.cc
@@ -295,7 +295,7 @@
 
 TEST(DFA, ReverseMatch) {
   int nfail = 0;
-  for (int i = 0; i < arraysize(reverse_tests); i++) {
+  for (size_t i = 0; i < arraysize(reverse_tests); i++) {
     const ReverseTest& t = reverse_tests[i];
     Regexp* re = Regexp::Parse(t.regexp, Regexp::LikePerl, NULL);
     ASSERT_TRUE(re != NULL);
@@ -350,7 +350,7 @@
 
 TEST(DFA, Callback) {
   int nfail = 0;
-  for (int i = 0; i < arraysize(callback_tests); i++) {
+  for (size_t i = 0; i < arraysize(callback_tests); i++) {
     const CallbackTest& t = callback_tests[i];
     Regexp* re = Regexp::Parse(t.regexp, Regexp::LikePerl, NULL);
     ASSERT_TRUE(re != NULL);