diff --git a/arch/ia64/sn/kernel/irq.c b/arch/ia64/sn/kernel/irq.c
index 96c31b4180c3..0c66dbdd1d72 100644
--- a/arch/ia64/sn/kernel/irq.c
+++ b/arch/ia64/sn/kernel/irq.c
@@ -5,7 +5,7 @@
  * License.  See the file "COPYING" in the main directory of this archive
  * for more details.
  *
- * Copyright (c) 2000-2007 Silicon Graphics, Inc.  All Rights Reserved.
+ * Copyright (c) 2000-2008 Silicon Graphics, Inc.  All Rights Reserved.
  */
 
 #include <linux/irq.h>
@@ -375,6 +375,7 @@ void sn_irq_fixup(struct pci_dev *pci_dev, struct sn_irq_info *sn_irq_info)
 	int cpu = nasid_slice_to_cpuid(nasid, slice);
 #ifdef CONFIG_SMP
 	int cpuphys;
+	irq_desc_t *desc;
 #endif
 
 	pci_dev_get(pci_dev);
@@ -391,6 +392,12 @@ void sn_irq_fixup(struct pci_dev *pci_dev, struct sn_irq_info *sn_irq_info)
 #ifdef CONFIG_SMP
 	cpuphys = cpu_physical_id(cpu);
 	set_irq_affinity_info(sn_irq_info->irq_irq, cpuphys, 0);
+	desc = irq_to_desc(sn_irq_info->irq_irq);
+	/*
+	 * Affinity was set by the PROM, prevent it from
+	 * being reset by the request_irq() path.
+	 */
+	desc->status |= IRQ_AFFINITY_SET;
 #endif
 }