diff --git a/xen/arch/x86/mtrr/generic.c b/xen/arch/x86/mtrr/generic.c
index 8da0c5b43c..93d35350a7 100644
--- a/xen/arch/x86/mtrr/generic.c
+++ b/xen/arch/x86/mtrr/generic.c
@@ -250,7 +250,7 @@ static void prepare_set(void)
 	/*  Save value of CR4 and clear Page Global Enable (bit 7)  */
 	if ( cpu_has_pge ) {
 		cr4 = read_cr4();
-		write_cr4(cr4 & (unsigned char) ~(1 << 7));
+		write_cr4(cr4 & ~X86_CR4_PGE);
 	}
 
 	/* Flush all TLBs via a mov %cr3, %reg; mov %reg, %cr3 */