diff --git a/rtl/objpas/classes/classes.inc b/rtl/objpas/classes/classes.inc
index 1e7becf4a8..dd146af4a0 100644
--- a/rtl/objpas/classes/classes.inc
+++ b/rtl/objpas/classes/classes.inc
@@ -265,6 +265,7 @@ begin
   inherited Create;
 {$ifdef FPC_HAS_FEATURE_THREADING}
     InterlockedIncrement(ThreadQueueLockCounter);
+    FThreadQueueLockCounted := true; { Guard against exception in descendant’s Create. }
 {$endif}
   if FExternalThread then
 {$ifdef FPC_HAS_FEATURE_THREADING}
@@ -289,7 +290,7 @@ begin
   RemoveQueuedEvents(Self);
   DoneSynchronizeEvent;
 {$ifdef FPC_HAS_FEATURE_THREADING}
-  if InterlockedDecrement(ThreadQueueLockCounter)=0 then
+  if FThreadQueueLockCounted and (InterlockedDecrement(ThreadQueueLockCounter)=0) then
     DoneCriticalSection(ThreadQueueLock);
 {$endif}
   { set CurrentThreadVar to Nil? }
diff --git a/rtl/objpas/classes/classesh.inc b/rtl/objpas/classes/classesh.inc
index 663429cd77..57cf3fd8db 100644
--- a/rtl/objpas/classes/classesh.inc
+++ b/rtl/objpas/classes/classesh.inc
@@ -2230,7 +2230,7 @@ type
     FReturnValue: Integer;
     FOnTerminate: TNotifyEvent;
     FFatalException: TObject;
-    FExternalThread: Boolean;
+    FExternalThread, FThreadQueueLockCounted: Boolean;
     FSynchronizeEntry: PThreadQueueEntry;
     class function GetCurrentThread: TThread; static;
     class function GetIsSingleProcessor: Boolean; static; inline;