diff --git a/js/src/jstask.h b/js/src/jstask.h
index 30bc009a2c2a..01ef393e9b6b 100644
--- a/js/src/jstask.h
+++ b/js/src/jstask.h
@@ -43,6 +43,7 @@ class JSBackgroundTask {
     friend class JSBackgroundThread;
     JSBackgroundTask* next;
   public:
+    virtual ~JSBackgroundTask() = 0;
     virtual void run() = 0;
 };