diff --git a/arch/x86/boot/a20.c b/arch/x86/boot/a20.c
index 38a1cad8a553..ff51b0ce4dfd 100644
--- a/arch/x86/boot/a20.c
+++ b/arch/x86/boot/a20.c
@@ -48,8 +48,9 @@ static int empty_8042(void)
    used as a test is the int $0x80 vector, which should be safe. */
 
 #define A20_TEST_ADDR	(4*0x80)
-#define A20_TEST_SHORT  32
-#define A20_TEST_LONG	2097152	/* 2^21 */
+
+#define A20_TEST_GS (*(volatile __seg_gs u32 *)A20_TEST_ADDR)
+#define A20_TEST_FS (*(volatile __seg_fs u32 *)(A20_TEST_ADDR+0x10))
 
 static int a20_test(int loops)
 {
@@ -57,20 +58,22 @@ static int a20_test(int loops)
 
 	set_fs(0xffff);
 
-	saved = ctr = rdgs32(A20_TEST_ADDR);
+	saved = ctr = A20_TEST_GS;
 
 	do {
-		wrgs32(++ctr, A20_TEST_ADDR);
-		io_delay();	/* Serialize and make delay constant */
-		barrier();	/* Compiler won't know about fs/gs overlap */
-		if (rdfs32(A20_TEST_ADDR+0x10) != ctr)
+		A20_TEST_GS = ++ctr;
+		io_delay();	/* Make constant delay */
+		if (A20_TEST_FS != ctr)
 			break;
 	} while (--loops);
 
-	wrgs32(saved, A20_TEST_ADDR);
+	A20_TEST_GS = saved;
 	return loops;
 }
 
+#define A20_TEST_SHORT  32
+#define A20_TEST_LONG	2097152	/* 2^21 */
+
 /* Quick test to see if A20 is already enabled */
 static int a20_test_short(void)
 {