diff --git a/lib/utils/locker.js b/lib/utils/locker.js
index c761ee28..0d8a1a3c 100644
--- a/lib/utils/locker.js
+++ b/lib/utils/locker.js
@@ -145,7 +145,7 @@ Locker.prototype.lock = function lock(arg1, arg2) {
 Locker.prototype.unlock = function unlock() {
   var job;
 
-  assert(this.busy);
+  assert(this.destroyed || this.busy);
 
   this.busy = false;
   this.current = null;
@@ -353,7 +353,7 @@ MappedLock.prototype.unlock = function unlock(key) {
     var jobs = self.jobs[key];
     var job;
 
-    assert(self.busy[key]);
+    assert(self.destroyed || self.busy[key]);
     delete self.busy[key];
 
     if (!jobs)