diff --git a/test/intrinsic_test.cpp b/test/intrinsic_test.cpp
index 17f04c4..32c05e7 100644
--- a/test/intrinsic_test.cpp
+++ b/test/intrinsic_test.cpp
@@ -25,7 +25,7 @@ int main()
     uint32 y4 = BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_4(x4);
     BOOST_TEST_EQ( y4, 0x44332211UL );
 
-    uint64 x8 = 0x1122334455667788U;
+    uint64 x8 = 0x1122334455667788ULL;
     uint64 y8 = BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_8(x8);
     BOOST_TEST_EQ( y8, 0x8877665544332211ULL );