diff --git a/arch/x86/include/asm/timer.h b/arch/x86/include/asm/timer.h
index e854c7ab4169..65228ccc5f0d 100644
--- a/arch/x86/include/asm/timer.h
+++ b/arch/x86/include/asm/timer.h
@@ -9,12 +9,14 @@
 
 unsigned long long native_sched_clock(void);
 unsigned long native_calibrate_tsc(void);
-
-#ifdef CONFIG_X86_32
-extern int timer_ack;
-#endif
 extern int recalibrate_cpu_khz(void);
 
+#if defined(CONFIG_X86_32) && defined(CONFIG_X86_IO_APIC)
+extern int timer_ack;
+#else
+# define timer_ack (0)
+#endif
+
 extern int no_timer_check;
 
 #ifndef CONFIG_PARAVIRT
diff --git a/arch/x86/kernel/time_32.c b/arch/x86/kernel/time_32.c
index acbaefd61e8e..7a26bcf887f6 100644
--- a/arch/x86/kernel/time_32.c
+++ b/arch/x86/kernel/time_32.c
@@ -23,7 +23,9 @@
 #include <asm/time.h>
 #include <asm/nmi.h>
 
+#if defined(CONFIG_X86_32) && defined(CONFIG_X86_IO_APIC)
 int timer_ack;
+#endif
 
 unsigned long profile_pc(struct pt_regs *regs)
 {
@@ -60,7 +62,7 @@ static irqreturn_t timer_interrupt(int irq, void *dev_id)
 	/* Keep nmi watchdog up to date */
 	inc_irq_stat(irq0_irqs);
 
-#ifdef CONFIG_X86_IO_APIC
+	/* Optimized out for !IO_APIC and x86_64 */
 	if (timer_ack) {
 		/*
 		 * Subtle, when I/O APICs are used we have to ack timer IRQ
@@ -73,7 +75,6 @@ static irqreturn_t timer_interrupt(int irq, void *dev_id)
 		inb(PIC_MASTER_POLL);
 		spin_unlock(&i8259A_lock);
 	}
-#endif
 
 	global_clock_event->event_handler(global_clock_event);
 
diff --git a/arch/x86/kernel/time_64.c b/arch/x86/kernel/time_64.c
index 45914f8844a7..35e0a925da56 100644
--- a/arch/x86/kernel/time_64.c
+++ b/arch/x86/kernel/time_64.c
@@ -51,6 +51,20 @@ static irqreturn_t timer_interrupt(int irq, void *dev_id)
 {
 	inc_irq_stat(irq0_irqs);
 
+	/* Optimized out for !IO_APIC and x86_64 */
+	if (timer_ack) {
+		/*
+		 * Subtle, when I/O APICs are used we have to ack timer IRQ
+		 * manually to deassert NMI lines for the watchdog if run
+		 * on an 82489DX-based system.
+		 */
+		spin_lock(&i8259A_lock);
+		outb(0x0c, PIC_MASTER_OCW3);
+		/* Ack the IRQ; AEOI will end it automatically. */
+		inb(PIC_MASTER_POLL);
+		spin_unlock(&i8259A_lock);
+	}
+
 	global_clock_event->event_handler(global_clock_event);
 
 #ifdef CONFIG_MCA