Index: sys/x86/x86/intr_machdep.c
===================================================================
--- sys/x86/x86/intr_machdep.c
+++ sys/x86/x86/intr_machdep.c
@@ -221,12 +221,13 @@
 int
 intr_register_source(struct intsrc *isrc)
 {
-	int error, vector;
+	u_int vector;
+	int error;
 
 	KASSERT(intr_pic_registered(isrc->is_pic), ("unregistered PIC"));
 	vector = isrc->is_pic->pic_vector(isrc);
-	KASSERT(vector < num_io_irqs, ("IRQ %d too large (%u irqs)", vector,
-	    num_io_irqs));
+	if (vector >= num_io_irqs)
+		return (EINVAL);
 	if (interrupt_sources[vector] != NULL)
 		return (EEXIST);
 	error = intr_event_create(&isrc->is_event, isrc, 0, vector,