diff --git a/lcl/asyncprocess.pp b/lcl/asyncprocess.pp
index bea3780912..a82f29bd1c 100644
--- a/lcl/asyncprocess.pp
+++ b/lcl/asyncprocess.pp
@@ -101,19 +101,13 @@ end;
 procedure TAsyncProcess.UnhookProcessHandle;
 begin
   if FProcessHandler <> nil then
-  begin
     RemoveProcessEventHandler(FProcessHandler);
-    FProcessHandler := nil;
-  end;
 end;
 
 procedure TAsyncProcess.UnhookPipeHandle;
 begin
   if FPipeHandler <> nil then
-  begin
     RemovePipeEventHandler(FPipeHandler);
-    FPipeHandler := nil;
-  end;
 end;
 
 procedure TAsyncProcess.HandlePipeInput(AData: PtrInt; AReasons: TPipeReasons);
diff --git a/lcl/include/intfbaselcl.inc b/lcl/include/intfbaselcl.inc
index 68e0e9ae46..dd96dc19cc 100644
--- a/lcl/include/intfbaselcl.inc
+++ b/lcl/include/intfbaselcl.inc
@@ -562,15 +562,15 @@ begin
   Result := false;
 end;
 
-procedure TWidgetSet.RemoveEventHandler(AHandler: PEventHandler);
+procedure TWidgetSet.RemoveEventHandler(var AHandler: PEventHandler);
 begin
 end;
 
-procedure TWidgetSet.RemoveProcessEventHandler(AHandler: PProcessEventHandler);
+procedure TWidgetSet.RemoveProcessEventHandler(var AHandler: PProcessEventHandler);
 begin
 end;
 
-procedure TWidgetSet.RemovePipeEventHandler(AHandler: PPipeEventHandler);
+procedure TWidgetSet.RemovePipeEventHandler(var AHandler: PPipeEventHandler);
 begin
 end;
 
diff --git a/lcl/include/lclintf.inc b/lcl/include/lclintf.inc
index 31483b14da..deab0edc37 100644
--- a/lcl/include/lclintf.inc
+++ b/lcl/include/lclintf.inc
@@ -393,17 +393,17 @@ begin
   Result := WidgetSet.ReleaseDesignerDC(hWnd, DC);
 end;
 
-procedure RemoveEventHandler(AHandler: PEventHandler);
+procedure RemoveEventHandler(var AHandler: PEventHandler);
 begin
   WidgetSet.RemoveEventHandler(AHandler);
 end;
 
-procedure RemoveProcessEventHandler(AHandler: PProcessEventHandler);
+procedure RemoveProcessEventHandler(var AHandler: PProcessEventHandler);
 begin
   WidgetSet.RemoveProcessEventHandler(AHandler);
 end;
 
-procedure RemovePipeEventHandler(AHandler: PPipeEventHandler);
+procedure RemovePipeEventHandler(var AHandler: PPipeEventHandler);
 begin
   WidgetSet.RemovePipeEventHandler(AHandler);
 end;
diff --git a/lcl/include/lclintfh.inc b/lcl/include/lclintfh.inc
index 6e149fc7a6..45cb68753b 100644
--- a/lcl/include/lclintfh.inc
+++ b/lcl/include/lclintfh.inc
@@ -107,9 +107,9 @@ function RadialPie(DC: HDC; x,y,width,height,sx,sy,ex,ey : Integer): Boolean; {$
 function RadialPieWithAngles(DC: HDC; X,Y,Width,Height,Angle1,Angle2: Integer): Boolean; {$IFDEF IF_BASE_MEMBER}virtual;{$ENDIF}
 function RegroupMenuItem(hndMenu: HMENU; GroupIndex: integer): Boolean; {$IFDEF IF_BASE_MEMBER}virtual;{$ENDIF}
 function ReleaseDesignerDC(hWnd: HWND; DC: HDC): Integer;  {$IFDEF IF_BASE_MEMBER}virtual;{$ENDIF}
-procedure RemoveEventHandler(AHandler: PEventHandler); {$IFDEF IF_BASE_MEMBER}virtual;{$ENDIF}
-procedure RemoveProcessEventHandler(AHandler: PProcessEventHandler); {$IFDEF IF_BASE_MEMBER}virtual;{$ENDIF}
-procedure RemovePipeEventHandler(AHandler: PPipeEventHandler); {$IFDEF IF_BASE_MEMBER}virtual;{$ENDIF}
+procedure RemoveEventHandler(var AHandler: PEventHandler); {$IFDEF IF_BASE_MEMBER}virtual;{$ENDIF}
+procedure RemoveProcessEventHandler(var AHandler: PProcessEventHandler); {$IFDEF IF_BASE_MEMBER}virtual;{$ENDIF}
+procedure RemovePipeEventHandler(var AHandler: PPipeEventHandler); {$IFDEF IF_BASE_MEMBER}virtual;{$ENDIF}
 function ReplaceBitmapMask(var Image, Mask: HBitmap; NewMask: HBitmap): boolean; {$IFDEF IF_BASE_MEMBER}virtual;{$ENDIF}
 function RequestInput(const InputCaption, InputPrompt : String; MaskInput : Boolean; var Value : String) : Boolean; {$IFDEF IF_BASE_MEMBER}virtual;{$ENDIF}
 
diff --git a/lcl/interfaces/gtk/gtklclintf.inc b/lcl/interfaces/gtk/gtklclintf.inc
index 444cb5b7ad..9bfe93fde4 100644
--- a/lcl/interfaces/gtk/gtklclintf.inc
+++ b/lcl/interfaces/gtk/gtklclintf.inc
@@ -61,7 +61,7 @@ begin
   Result := lEventHandler;
 end;
 
-procedure TGtkWidgetSet.RemoveEventHandler(AHandler: PEventHandler);
+procedure TGtkWidgetSet.RemoveEventHandler(var AHandler: PEventHandler);
 var
   lEventHandler: PWaitHandleEventHandler absolute AHandler;
 begin
@@ -74,6 +74,7 @@ begin
   if lEventHandler^.NextHandler <> nil then
     lEventHandler^.NextHandler^.PrevHandler := lEventHandler^.PrevHandler;
   Dispose(lEventHandler);
+  AHandler := nil;
 end;
 
 procedure TGtkWidgetSet.SetEventHandlerFlags(AHandler: PEventHandler; NewFlags: dword);
@@ -124,13 +125,14 @@ begin
   lPipeEventInfo^.OnEvent(lPipeEventInfo^.UserData, lReasons);
 end;
 
-procedure TGtkWidgetSet.RemovePipeEventHandler(AHandler: PPipeEventHandler);
+procedure TGtkWidgetSet.RemovePipeEventHandler(var AHandler: PPipeEventHandler);
 var
   lPipeEventInfo: PPipeEventInfo absolute AHandler;
 begin
   if AHandler = nil then exit;
   RemoveEventHandler(lPipeEventInfo^.Handler);
   Dispose(lPipeEventInfo);
+  AHandler := nil;
 end;
 
 function TGtkWidgetSet.AddProcessEventHandler(AHandle: THandle;
@@ -151,7 +153,7 @@ begin
   Result := lHandler;
 end;
 
-procedure TGtkWidgetSet.RemoveProcessEventHandler(AHandler: PProcessEventHandler);
+procedure TGtkWidgetSet.RemoveProcessEventHandler(var AHandler: PProcessEventHandler);
 var
   lHandler: PChildSignalEventHandler absolute AHandler;
 begin
@@ -163,6 +165,7 @@ begin
   if lHandler^.NextHandler <> nil then
     lHandler^.NextHandler^.PrevHandler := lHandler^.PrevHandler;
   Dispose(lHandler);
+  AHandler := nil;
 end;
 
 {------------------------------------------------------------------------------
diff --git a/lcl/interfaces/gtk/gtklclintfh.inc b/lcl/interfaces/gtk/gtklclintfh.inc
index 7059ae97a6..041da2b241 100644
--- a/lcl/interfaces/gtk/gtklclintfh.inc
+++ b/lcl/interfaces/gtk/gtklclintfh.inc
@@ -50,9 +50,9 @@ function GetListBoxItemRect(ListBox: TComponent; Index: integer; var ARect: TRec
 
 function IntfSendsUTF8KeyPress: boolean; override;
 
-procedure RemoveEventHandler(AHandler: PEventHandler); override;
-procedure RemovePipeEventHandler(AHandler: PPipeEventHandler); override;
-procedure RemoveProcessEventHandler(AHandler: PProcessEventHandler); override;
+procedure RemoveEventHandler(var AHandler: PEventHandler); override;
+procedure RemovePipeEventHandler(var AHandler: PPipeEventHandler); override;
+procedure RemoveProcessEventHandler(var AHandler: PProcessEventHandler); override;
 function ReplaceBitmapMask(var Image, Mask: HBitmap; NewMask: HBitmap): boolean; override;
 
 procedure SetEventHandlerFlags(AHandler: PEventHandler; NewFlags: dword); override;
diff --git a/lcl/interfaces/win32/win32lclintf.inc b/lcl/interfaces/win32/win32lclintf.inc
index 8b58714c1f..4096b54f36 100644
--- a/lcl/interfaces/win32/win32lclintf.inc
+++ b/lcl/interfaces/win32/win32lclintf.inc
@@ -55,7 +55,7 @@ begin
   Result := lListIndex;
 end;
 
-procedure TWin32WidgetSet.RemoveEventHandler(AHandler: PEventHandler);
+procedure TWin32WidgetSet.RemoveEventHandler(var AHandler: PEventHandler);
 var
   lListIndex: pdword absolute AHandler;
   I: dword;
@@ -76,6 +76,7 @@ begin
   end;
   Dec(FWaitHandleCount);
   Dispose(lListIndex);
+  AHandler := nil;
 end;
 
 function TWin32WidgetSet.AddPipeEventHandler(AHandle: THandle; 
@@ -96,7 +97,7 @@ begin
   Result := lHandler;
 end;
 
-procedure TWin32WidgetSet.RemovePipeEventHandler(AHandler: PPipeEventHandler);
+procedure TWin32WidgetSet.RemovePipeEventHandler(var AHandler: PPipeEventHandler);
 var
   lHandler: PPipeEventInfo absolute AHandler;
 begin
@@ -108,6 +109,7 @@ begin
   if lHandler^.Next <> nil then
     lHandler^.Next^.Prev := lHandler^.Prev;
   Dispose(lHandler);
+  AHandler := nil;
 end;
 
 function TWin32WidgetSet.AddProcessEventHandler(AHandle: THandle;
@@ -135,13 +137,14 @@ begin
   lProcessEvent^.OnEvent(lProcessEvent^.UserData, cerExit, exitcode);
 end;
 
-procedure TWin32WidgetSet.RemoveProcessEventHandler(AHandler: PProcessEventHandler);
+procedure TWin32WidgetSet.RemoveProcessEventHandler(var AHandler: PProcessEventHandler);
 var
   lProcessEvent: PProcessEvent absolute AHandler;
 begin
   if AHandler = nil then exit;
   RemoveEventHandler(lProcessEvent^.Handler);
   Dispose(lProcessEvent);
+  AHandler := nil;
 end;
 
 procedure TWin32WidgetSet.DrawArrow(Arrow: TComponent; Canvas: TPersistent);
diff --git a/lcl/interfaces/win32/win32lclintfh.inc b/lcl/interfaces/win32/win32lclintfh.inc
index b3e411fc07..3d5ab4c818 100644
--- a/lcl/interfaces/win32/win32lclintfh.inc
+++ b/lcl/interfaces/win32/win32lclintfh.inc
@@ -42,9 +42,9 @@ function GetAcceleratorString(const AVKey: Byte; const AShiftState: TShiftState)
 function GetControlConstraints(Constraints: TObject): boolean; override;
 function GetListBoxIndexAtY(ListBox: TComponent; y: integer): integer; override;
 
-procedure RemoveEventHandler(AHandler: PEventHandler); override;
-procedure RemovePipeEventHandler(AHandler: PPipeEventHandler); override;
-procedure RemoveProcessEventHandler(AHandler: PProcessEventHandler); override;
+procedure RemoveEventHandler(var AHandler: PEventHandler); override;
+procedure RemovePipeEventHandler(var AHandler: PPipeEventHandler); override;
+procedure RemoveProcessEventHandler(var AHandler: PProcessEventHandler); override;
 
 
 //##apiwiz##eps##   // Do not remove, no wizard declaration after this line