--- a/usr/src/uts/common/fs/zfs/metaslab.c	Tue Nov 10 11:43:02 2009 +0530
+++ b/usr/src/uts/common/fs/zfs/metaslab.c	Mon Nov 09 23:34:30 2009 -0700
@@ -196,7 +196,12 @@
 {
 	ASSERT(mg->mg_prev == NULL);
 	ASSERT(mg->mg_next == NULL);
-	ASSERT(mg->mg_activation_count + mg->mg_vd->vdev_removing == 0);
+	/*
+	 * We may have gone below zero with the activation count
+	 * either because we never activated in the first place or
+	 * because we're done, and possibly removing the vdev.
+	 */
+	ASSERT(mg->mg_activation_count <= 0);
 
 	avl_destroy(&mg->mg_metaslab_tree);
 	mutex_destroy(&mg->mg_lock);