diff --git a/dom/ipc/ProcessPriorityManager.cpp b/dom/ipc/ProcessPriorityManager.cpp
index 04e745b3b512c..fc3038e577ae5 100644
--- a/dom/ipc/ProcessPriorityManager.cpp
+++ b/dom/ipc/ProcessPriorityManager.cpp
@@ -219,7 +219,8 @@ class ProcessPriorityManager MOZ_FINAL
   nsWeakPtr mMemoryMinimizerRunnable;
 };
 
-NS_IMPL_ISUPPORTS2(ProcessPriorityManager, nsIObserver, nsIDOMEventListener)
+NS_IMPL_ISUPPORTS3(ProcessPriorityManager, nsIObserver,
+                   nsIDOMEventListener, nsITimerCallback)
 
 ProcessPriorityManager::ProcessPriorityManager()
   : mProcessPriority(ProcessPriority(-1))