diff --git a/format_test.cc b/format_test.cc
index 262c73ea..be510da7 100644
--- a/format_test.cc
+++ b/format_test.cc
@@ -686,6 +686,7 @@ TEST(FormatterTest, HashFlag) {
   EXPECT_EQ("42", str(Format("{0:#}") << 42));
   EXPECT_EQ("-42", str(Format("{0:#}") << -42));
   EXPECT_EQ("0x42", str(Format("{0:#x}") << 0x42));
+  EXPECT_EQ("0X42", str(Format("{0:#X}") << 0x42));
   EXPECT_EQ("-0x42", str(Format("{0:#x}") << -0x42));
   EXPECT_EQ("042", str(Format("{0:#o}") << 042));
   EXPECT_EQ("-042", str(Format("{0:#o}") << -042));