diff --git a/certificate_checker_unittest.cc b/certificate_checker_unittest.cc
index a3d7465..5d4d8f0 100644
--- a/certificate_checker_unittest.cc
+++ b/certificate_checker_unittest.cc
@@ -61,7 +61,7 @@
   // Parameters of our mock certificate digest.
   int depth_;
   unsigned int length_;
-  unsigned char digest_[4];
+  uint8_t digest_[4];
   string digest_hex_;
   string diff_digest_hex_;
   string cert_key_prefix_;