diff --git a/components/fpdebug/fpdbgclasses.pp b/components/fpdebug/fpdbgclasses.pp
index 7f226025ef..2e3a4ceeb4 100644
--- a/components/fpdebug/fpdbgclasses.pp
+++ b/components/fpdebug/fpdbgclasses.pp
@@ -1000,6 +1000,7 @@ var
   Len, i: Integer;
   BList: TFpInternalBreakpointArray;
 begin
+  {$IFDEF FPDEBUG_THREAD_CHECK}AssertFpDebugThreadIdNotMain('TBreakLocationMap.AddLocotion');{$ENDIF}
   LocData := GetDataPtr(ALocation);
 
   if LocData <> nil then begin
@@ -1046,6 +1047,7 @@ var
   LocData: PInternalBreakLocationEntry;
   Len, i: Integer;
 begin
+  {$IFDEF FPDEBUG_THREAD_CHECK}AssertFpDebugThreadIdNotMain('TBreakLocationMap.RemoveLocotion');{$ENDIF}
   LocData := GetDataPtr(ALocation);
   if LocData = nil then begin
     DebugLn(DBG_WARNINGS or DBG_BREAKPOINTS, ['Missing breakpoint for loc ', FormatAddress(ALocation)]);
@@ -1126,6 +1128,7 @@ end;
 
 function TBreakLocationMap.GetEnumerator: TBreakLocationMapEnumerator;
 begin
+  {$IFDEF FPDEBUG_THREAD_CHECK}AssertFpDebugThreadId('TBreakLocationMap.GetEnumerator');{$ENDIF}
   Result := TBreakLocationMapEnumerator.Create(Self);
 end;
 
@@ -3123,6 +3126,7 @@ procedure TFpInternalBreakpoint.ResetBreak;
 var
   i: Integer;
 begin
+  {$IFDEF FPDEBUG_THREAD_CHECK}AssertFpDebugThreadId('TFpInternalBreakpoint.ResetBreak');{$ENDIF}
   if FProcess = nil then
     exit;
   for i := 0 to High(FLocation) do
@@ -3133,6 +3137,7 @@ procedure TFpInternalBreakpoint.SetBreak;
 var
   i: Integer;
 begin
+  {$IFDEF FPDEBUG_THREAD_CHECK}AssertFpDebugThreadId('TFpInternalBreakpoint.SetBreak');{$ENDIF}
   if FProcess = nil then
     exit;
   for i := 0 to High(FLocation) do
@@ -3228,6 +3233,7 @@ var
   R: Boolean;
   i: Integer;
 begin
+  {$IFDEF FPDEBUG_THREAD_CHECK}AssertFpDebugThreadId('TFpInternalWatchpoint.SetBreak');{$ENDIF}
   if FProcess = nil then
     exit;
   //TODO: read current mem content. So in case of overlap it can be checked
@@ -3259,6 +3265,7 @@ end;
 
 procedure TFpInternalWatchpoint.ResetBreak;
 begin
+  {$IFDEF FPDEBUG_THREAD_CHECK}AssertFpDebugThreadId('TFpInternalWatchpoint.ResetBreak');{$ENDIF}
   if FProcess = nil then
     exit;
 
diff --git a/components/fpdebug/fpdbgcommon.pas b/components/fpdebug/fpdbgcommon.pas
index 8f022d00d8..e507c3d190 100644
--- a/components/fpdebug/fpdbgcommon.pas
+++ b/components/fpdebug/fpdbgcommon.pas
@@ -4,6 +4,8 @@ unit FpDbgCommon;
 
 interface
 
+uses Classes;
+
 type
 // Target information, could be different from host debugger
   TMachineType = (mtNone, mtSPARC, mt386, mt68K, mtPPC, mtPPC64, mtARM, mtARM64,
@@ -23,6 +25,13 @@ type
 // Use when target information not yet loaded - assumes that debug target is the same as host
 function hostDescriptor: TTargetDescriptor;
 
+{$IFDEF FPDEBUG_THREAD_CHECK}
+procedure AssertFpDebugThreadId(const AName: String);
+procedure AssertFpDebugThreadIdNotMain(const AName: String);
+procedure SetCurrentFpDebugThreadIdForAssert(AnId: TThreadID);
+property CurrentFpDebugThreadIdForAssert: TThreadID write SetCurrentFpDebugThreadIdForAssert;
+{$ENDIF}
+
 implementation
 
 function hostDescriptor: TTargetDescriptor;
@@ -49,5 +58,30 @@ begin
   end;
 end;
 
+{$IFDEF FPDEBUG_THREAD_CHECK}
+var
+  FCurrentFpDebugThreadIdForAssert: TThreadID;
+  FCurrentFpDebugThreadIdValidForAssert: Boolean;
+
+procedure AssertFpDebugThreadId(const AName: String);
+begin
+  if FCurrentFpDebugThreadIdValidForAssert then
+    assert(GetCurrentThreadId = FCurrentFpDebugThreadIdForAssert, AName);
+end;
+
+procedure AssertFpDebugThreadIdNotMain(const AName: String);
+begin
+  AssertFpDebugThreadId(AName);
+  assert(GetCurrentThreadId<>MainThreadID, AName + ' runnig outside main thread');
+end;
+
+procedure SetCurrentFpDebugThreadIdForAssert(AnId: TThreadID);
+begin
+  FCurrentFpDebugThreadIdForAssert := AnId;
+  FCurrentFpDebugThreadIdValidForAssert := True;
+end;
+
+{$ENDIF}
+
 end.
 
diff --git a/components/lazdebuggers/lazdebuggerfp/fpdebugdebugger.pas b/components/lazdebuggers/lazdebuggerfp/fpdebugdebugger.pas
index dd6d9e692e..b825ee9376 100644
--- a/components/lazdebuggers/lazdebuggerfp/fpdebugdebugger.pas
+++ b/components/lazdebuggers/lazdebuggerfp/fpdebugdebugger.pas
@@ -38,6 +38,7 @@ uses
   DbgIntfBaseTypes, DbgIntfDebuggerBase,
   FpDebugDebuggerUtils, FpDebugDebuggerWorkThreads,
   // FpDebug
+  {$IFDEF FPDEBUG_THREAD_CHECK} FpDbgCommon, {$ENDIF}
   FpDbgClasses, FpDbgInfo, FpErrorMessages, FpPascalBuilder, FpdMemoryTools,
   FpPascalParser, FPDbgController, FpDbgDwarfDataClasses, FpDbgDwarfFreePascal,
   FpDbgDwarf, FpDbgUtil;
@@ -2923,6 +2924,7 @@ end;
 procedure TFpDebugDebugger.FreeDebugThread;
 begin
   FWorkQueue.TerminateAllThreads(True);
+  {$IFDEF FPDEBUG_THREAD_CHECK} CurrentFpDebugThreadIdForAssert := MainThreadID;{$ENDIF}
   Application.ProcessMessages; // run the AsyncMethods
 end;
 
@@ -3111,6 +3113,7 @@ begin
     end;
     FWorkQueue.Clear;
     FWorkQueue.ThreadCount := 1;
+    {$IFDEF FPDEBUG_THREAD_CHECK} CurrentFpDebugThreadIdForAssert := FWorkQueue.Threads[0].ThreadID;{$ENDIF}
     WorkItem := TFpThreadWorkerControllerRun.Create(Self);
     FWorkQueue.PushItem(WorkItem);
     FWorkQueue.WaitForItem(WorkItem, True);
@@ -3659,6 +3662,7 @@ begin
     end;
   FWorkQueue.TerminateAllThreads(True);
   Application.ProcessMessages; // run the AsyncMethods
+  {$IFDEF FPDEBUG_THREAD_CHECK} CurrentFpDebugThreadIdForAssert := MainThreadID;{$ENDIF}
 
   Application.RemoveAsyncCalls(Self);
   FreeAndNil(FDbgController);