diff --git a/xen/arch/x86/x86_emulate/x86_emulate.h b/xen/arch/x86/x86_emulate/x86_emulate.h
index 698750267a..d92be69d84 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.h
+++ b/xen/arch/x86/x86_emulate/x86_emulate.h
@@ -620,7 +620,7 @@ struct x86_emulate_ctxt
  * below).
  * Hence no separate #define-s get added.
  */
-#define X86EMUL_OPC_EXT_MASK         0xffff0000
+#define X86EMUL_OPC_EXT_MASK         0xffff0000U
 #define X86EMUL_OPC(ext, byte)       ((uint8_t)(byte) | \
                                       MASK_INSR((ext), X86EMUL_OPC_EXT_MASK))
 /*