Index: sys/x86/xen/xen_arch_intr.c
===================================================================
--- sys/x86/xen/xen_arch_intr.c
+++ sys/x86/xen/xen_arch_intr.c
@@ -219,6 +219,9 @@
     struct xenisrc *isrc)
 {
 
+	if (isrc->xi_cookie != NULL)
+		return (EINVAL);
+
 	return (intr_add_handler(name, isrc->xi_arch.xai_vector, filter,
 	    handler, arg, flags, &isrc->xi_cookie, 0));
 }
Index: sys/xen/xen_intr.c
===================================================================
--- sys/xen/xen_intr.c
+++ sys/xen/xen_intr.c
@@ -279,7 +279,7 @@
 
 	if (isrc != NULL) {
 		mtx_unlock(&xen_intr_x86_lock);
-		return (isrc);
+		goto out;
 	}
 
 	if (xen_intr_auto_vector_count >= NR_EVENT_CHANNELS) {
@@ -307,6 +307,12 @@
 		return (NULL);
 	}
 
+out:
+	KASSERT(!xen_arch_intr_has_handlers(isrc),
+	    ("Allocator called, but xenisrc still in use"));
+
+	isrc->xi_cookie = NULL;
+
 	return (isrc);
 }
 
@@ -322,8 +328,6 @@
 {
 
 	mtx_lock(&xen_intr_isrc_lock);
-	KASSERT(xen_arch_intr_has_handlers(isrc),
-	    ("Release called, but xenisrc still in use"));
 	evtchn_mask_port(isrc->xi_port);
 	evtchn_clear_port(isrc->xi_port);
 
@@ -345,6 +349,9 @@
 	/* not reachable from xen_intr_port_to_isrc[], therefore unlock */
 	mtx_unlock(&xen_intr_isrc_lock);
 
+	if (isrc->xi_cookie != NULL)
+		xen_arch_intr_remove_handler(isrc);
+
 	isrc->xi_cpu = 0;
 	isrc->xi_port = ~0U;
 	isrc->xi_cookie = NULL;
@@ -1169,8 +1176,6 @@
 	}
 	mtx_unlock(&xen_intr_isrc_lock);
 
-	if (isrc->xi_cookie != NULL)
-		xen_arch_intr_remove_handler(isrc);
 	xen_intr_release_isrc(isrc);
 }
 
@@ -1210,7 +1215,7 @@
 	int error;
 
 	isrc = xen_intr_isrc_from_handle(handle);
-	if (isrc == NULL || isrc->xi_cookie != NULL)
+	if (isrc == NULL)
 		return (EINVAL);
 
 	error = xen_arch_intr_add_handler(name, filter, handler, arg,