diff --git a/xen/arch/x86/acpi/cpufreq/acpi.c b/xen/arch/x86/acpi/cpufreq/acpi.c
index c6d7d02faa..0c25376406 100644
--- a/xen/arch/x86/acpi/cpufreq/acpi.c
+++ b/xen/arch/x86/acpi/cpufreq/acpi.c
@@ -25,7 +25,7 @@ enum {
     SYSTEM_IO_CAPABLE,
 };
 
-#define INTEL_MSR_RANGE         (0xffffull)
+#define INTEL_MSR_RANGE         0xffffULL
 
 static bool __read_mostly acpi_pstate_strict;
 boolean_param("acpi_pstate_strict", acpi_pstate_strict);