diff --git a/format-test.cc b/format-test.cc
index e18e4aeb..1438e470 100644
--- a/format-test.cc
+++ b/format-test.cc
@@ -234,7 +234,7 @@ TEST(ArrayTest, MoveCtor) {
   // Move should rip the guts of the first array.
   EXPECT_EQ(inline_buffer_ptr, &array[0]);
   EXPECT_EQ("testab", std::string(&array2[0], array2.size()));
-  EXPECT_GT(array2.capacity(), 5);
+  EXPECT_GT(array2.capacity(), 5u);
 }
 
 void CheckMoveAssignArray(const char *str, Array<char, 5> &array) {