diff --git a/http2/hpack/varint/hpack_varint_round_trip_test.cc b/http2/hpack/varint/hpack_varint_round_trip_test.cc
index 45eaef2..3299d5e 100644
--- a/http2/hpack/varint/hpack_varint_round_trip_test.cc
+++ b/http2/hpack/varint/hpack_varint_round_trip_test.cc
@@ -113,7 +113,8 @@
     ASSERT_LT(0u, buffer_.size());
 
     const uint8_t prefix_mask = (1 << prefix_length_) - 1;
-    ASSERT_EQ(buffer_[0], buffer_[0] & prefix_mask);
+    ASSERT_EQ(static_cast<uint8_t>(buffer_[0]),
+              static_cast<uint8_t>(buffer_[0]) & prefix_mask);
   }
 
   void Encode(uint64_t value, uint8_t prefix_length) {