diff --git a/sys/alpha/isa/isa.c b/sys/alpha/isa/isa.c
index 48404b8ce5b..95c7d58ab23 100644
--- a/sys/alpha/isa/isa.c
+++ b/sys/alpha/isa/isa.c
@@ -338,6 +338,9 @@ isa_setup_intr(device_t dev, device_t child,
 		return platform.isa_setup_intr(dev, child, irq, flags, 
 			intr, arg, cookiep);	
 
+	if (irq == NULL)
+		return ENODEV;
+
 	error = rman_activate_resource(irq);
 	if (error)
 		return error;