diff --git a/xpcom/glue/Monitor.h b/xpcom/glue/Monitor.h
index 62e20f58342f..60750acb3328 100644
--- a/xpcom/glue/Monitor.h
+++ b/xpcom/glue/Monitor.h
@@ -96,7 +96,6 @@ private:
   MonitorAutoLock(const MonitorAutoLock&);
   MonitorAutoLock& operator=(const MonitorAutoLock&);
   static void* operator new(size_t) CPP_THROW_NEW;
-  static void operator delete(void*);
 
   Monitor* mMonitor;
 };
@@ -127,7 +126,6 @@ private:
   MonitorAutoUnlock(const MonitorAutoUnlock&);
   MonitorAutoUnlock& operator=(const MonitorAutoUnlock&);
   static void* operator new(size_t) CPP_THROW_NEW;
-  static void operator delete(void*);
 
   Monitor* mMonitor;
 };
diff --git a/xpcom/glue/Mutex.h b/xpcom/glue/Mutex.h
index 7544b7b5c3d1..a5ed05f36a35 100644
--- a/xpcom/glue/Mutex.h
+++ b/xpcom/glue/Mutex.h
@@ -174,7 +174,6 @@ private:
   BaseAutoLock(BaseAutoLock&);
   BaseAutoLock& operator=(BaseAutoLock&);
   static void* operator new(size_t) CPP_THROW_NEW;
-  static void operator delete(void*);
 
   T* mLock;
   MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
@@ -212,7 +211,6 @@ private:
   BaseAutoUnlock(BaseAutoUnlock&);
   BaseAutoUnlock& operator=(BaseAutoUnlock&);
   static void* operator new(size_t) CPP_THROW_NEW;
-  static void operator delete(void*);
 
   T* mLock;
   MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
diff --git a/xpcom/glue/ReentrantMonitor.h b/xpcom/glue/ReentrantMonitor.h
index e3e9bbaeb7bf..0798fe2af3e5 100644
--- a/xpcom/glue/ReentrantMonitor.h
+++ b/xpcom/glue/ReentrantMonitor.h
@@ -198,7 +198,6 @@ private:
   ReentrantMonitorAutoEnter(const ReentrantMonitorAutoEnter&);
   ReentrantMonitorAutoEnter& operator=(const ReentrantMonitorAutoEnter&);
   static void* operator new(size_t) CPP_THROW_NEW;
-  static void operator delete(void*);
 
   mozilla::ReentrantMonitor* mReentrantMonitor;
 };
@@ -240,7 +239,6 @@ private:
   ReentrantMonitorAutoExit(const ReentrantMonitorAutoExit&);
   ReentrantMonitorAutoExit& operator=(const ReentrantMonitorAutoExit&);
   static void* operator new(size_t) CPP_THROW_NEW;
-  static void operator delete(void*);
 
   ReentrantMonitor* mReentrantMonitor;
 };