diff --git a/ide/allcompileroptions.lfm b/ide/allcompileroptions.lfm
index 52a9d8bb3b..072b77bd1f 100644
--- a/ide/allcompileroptions.lfm
+++ b/ide/allcompileroptions.lfm
@@ -6,7 +6,7 @@ object frmAllCompilerOptions: TfrmAllCompilerOptions
   Caption = 'frmAllCompilerOptions'
   ClientHeight = 497
   ClientWidth = 622
-  OnShow = FormShow
+  OnCreate = FormCreate
   LCLVersion = '1.3'
   object sbAllOptions: TScrollBox
     Left = 0
diff --git a/ide/allcompileroptions.pas b/ide/allcompileroptions.pas
index c17a872ddf..c3a28424ee 100644
--- a/ide/allcompileroptions.pas
+++ b/ide/allcompileroptions.pas
@@ -23,7 +23,7 @@ type
     procedure btnResetOptionsFilterClick(Sender: TObject);
     procedure cbShowModifiedClick(Sender: TObject);
     procedure edOptionsFilterChange(Sender: TObject);
-    procedure FormShow(Sender: TObject);
+    procedure FormCreate(Sender: TObject);
   private
     FIdleConnected: Boolean;
     FOptionsReader: TCompilerOptReader;
@@ -66,6 +66,7 @@ end;
 
 destructor TfrmAllCompilerOptions.Destroy;
 begin
+  IdleConnected:=false;
   FGeneratedControls.Clear;
   FreeAndNil(FGeneratedControls);
   inherited Destroy;
@@ -76,7 +77,7 @@ begin
   Result := FOptionsReader.ToCustomOptions(aStrings, cbUseComments.Checked);
 end;
 
-procedure TfrmAllCompilerOptions.FormShow(Sender: TObject);
+procedure TfrmAllCompilerOptions.FormCreate(Sender: TObject);
 begin
   Caption:=lisAllOptions;
   edOptionsFilter.Hint := lisFilterTheAvailableOptionsList;
@@ -110,6 +111,8 @@ end;
 
 procedure TfrmAllCompilerOptions.SetIdleConnected(AValue: Boolean);
 begin
+  if csDestroying in ComponentState then
+    AValue:=false;
   if FIdleConnected = AValue then exit;
   FIdleConnected := AValue;
   if FIdleConnected then
@@ -132,9 +135,10 @@ var
   StartTime: TDateTime;
 begin
   IdleConnected := False;
+  if FOptionsThread=nil then exit;
   Screen.Cursor := crHourGlass;
   try
-    FOptionsThread.WaitFor;            // Make sure the options are read.
+    FOptionsThread.EndParsing;            // Make sure the options are read.
     if FOptionsReader.ErrorMsg <> '' then
       DebugLn(FOptionsReader.ErrorMsg)
     else begin
diff --git a/ide/compiler.pp b/ide/compiler.pp
index 059edc85c2..5a59e2465a 100644
--- a/ide/compiler.pp
+++ b/ide/compiler.pp
@@ -209,6 +209,8 @@ type
     procedure Clear;
     function UpdateTargetParam: Boolean;
     function ReadAndParseOptions: TModalResult;
+    function ParseOptions(OutputI, OutputH: TStringList): TModalResult;
+    procedure ReadCompiler(CompPath, Params: string; out OutputI, OutputH: TStringList);
     function FilterOptions(aFilter: string; aOnlySelected: Boolean): Boolean;
     function FindOptionById(aId: integer): TCompilerOpt;
     function FromCustomOptions(aStrings: TStrings): TModalResult;
@@ -228,12 +230,20 @@ type
   private
     fReader: TCompilerOptReader;
     fReadTime: TDateTime;
+    fCompPath: string;
+    fCompParams: string;
+    fOutputI: TStringList;
+    fOutputH: TStringList;
+    fStartedOnce: boolean;
     function GetErrorMsg: string;
+    procedure Clear; // (main thread)
   protected
     procedure Execute; override;
   public
     constructor Create(aReader: TCompilerOptReader);
     destructor Destroy; override;
+    procedure StartParsing; // (main thread)
+    procedure EndParsing; // (main thread)
   public
     property ReadTime: TDateTime read fReadTime;
     property ErrorMsg: string read GetErrorMsg;
@@ -1166,29 +1176,43 @@ function TCompilerOptReader.ReadAndParseOptions: TModalResult;
 // fpc -Fr$(FPCMsgFile) -h
 // fpc -Fr$(FPCMsgFile) -i
 var
-  Lines: TStringList;
+  OutputI: TStringList;
+  OutputH: TStringList;
+begin
+  if fCompilerExecutable = '' then
+    fCompilerExecutable := 'fpc';        // Let's hope "fpc" is found in PATH.
+  try
+    ReadCompiler(fCompilerExecutable, fParsedTarget, OutputI, OutputH);
+    Result:=ParseOptions(OutputI, OutputH);
+  finally
+    OutputI.Free;
+    OutputH.Free;
+  end;
+end;
+
+function TCompilerOptReader.ParseOptions(OutputI, OutputH: TStringList
+  ): TModalResult;
 begin
   OptionIdCounter := 0;
   fErrorMsg := '';
-  if fCompilerExecutable = '' then
-    fCompilerExecutable := 'fpc';        // Let's hope "fpc" is found in PATH.
+  if OutputI = Nil then Exit(mrCancel);
+  Result := ParseI(OutputI);
+  if Result <> mrOK then Exit;
+  if OutputH = Nil then Exit(mrCancel);
+  Result := ParseH(OutputH);
+end;
+
+procedure TCompilerOptReader.ReadCompiler(CompPath, Params: string; out
+  OutputI, OutputH: TStringList);
+begin
+  OutputH:=nil;
+  OutputI:=nil;
+  if CompPath = '' then
+    CompPath := 'fpc';        // Let's hope "fpc" is found in PATH.
   // FPC with option -i
-  Lines:=RunTool(fCompilerExecutable, fParsedTarget + ' -i');
-  try
-    if Lines = Nil then Exit(mrCancel);
-    Result := ParseI(Lines);
-    if Result <> mrOK then Exit;
-  finally
-    Lines.Free;
-  end;
+  OutputI:=RunTool(CompPath, Params + ' -i');
   // FPC with option -h
-  Lines:=RunTool(fCompilerExecutable, fParsedTarget + ' -h');
-  try
-    if Lines = Nil then Exit(mrCancel);
-    Result := ParseH(Lines);
-  finally
-    Lines.Free;
-  end;
+  OutputH:=RunTool(CompPath, Params + ' -h');
 end;
 
 function TCompilerOptReader.FilterOptions(aFilter: string; aOnlySelected: Boolean): Boolean;
@@ -1364,12 +1388,15 @@ constructor TCompilerOptThread.Create(aReader: TCompilerOptReader);
 begin
   inherited Create(True);
   //FreeOnTerminate:=True;
+  fStartedOnce:=false;
   fReader:=aReader;
-  fReader.UpdateTargetParam;
 end;
 
 destructor TCompilerOptThread.Destroy;
 begin
+  if fStartedOnce then
+    WaitFor;
+  Clear;
   inherited Destroy;
 end;
 
@@ -1378,17 +1405,51 @@ begin
   Result := fReader.ErrorMsg;
 end;
 
+procedure TCompilerOptThread.Clear;
+begin
+  FreeAndNil(fOutputH);
+  FreeAndNil(fOutputI);
+end;
+
+procedure TCompilerOptThread.StartParsing;
+begin
+  if fStartedOnce then
+    WaitFor;
+  fReader.CompilerExecutable:=LazarusIDE.GetFPCompilerFilename;;
+  fReader.UpdateTargetParam;
+  fCompPath:=fReader.CompilerExecutable;
+  fCompParams:=fReader.ParsedTarget;
+  Start;
+  fStartedOnce:=true;
+end;
+
+procedure TCompilerOptThread.EndParsing;
+begin
+  if fStartedOnce then
+    WaitFor;
+  if (fOutputI<>nil) or (fOutputH<>nil) then begin
+    try
+      fReader.ParseOptions(fOutputI,fOutputH);
+    except
+      on E: Exception do
+        fReader.ErrorMsg := 'Error parsing compiler output: '+E.Message;
+    end;
+    Clear;
+  end;
+end;
+
 procedure TCompilerOptThread.Execute;
 var
   StartTime: TDateTime;
 begin
   StartTime := Now;
   try
-    fReader.CompilerExecutable := LazarusIDE.GetFPCompilerFilename;
-    fReader.ReadAndParseOptions;
+    if fOutputI<>nil then exit;
+    if fOutputH<>nil then exit;
+    fReader.ReadCompiler(fCompPath,fCompParams,fOutputI,fOutputH);
   except
     on E: Exception do
-      fReader.ErrorMsg := 'Error parsing options: '+E.Message;
+      fReader.ErrorMsg := 'Error reading compiler: '+E.Message;
   end;
   fReadTime := Now-StartTime;
 end;
diff --git a/ide/customdefines.pas b/ide/customdefines.pas
index 7e886961cb..8f1404c6d8 100644
--- a/ide/customdefines.pas
+++ b/ide/customdefines.pas
@@ -161,7 +161,7 @@ begin
   IdleConnected := False;
   Screen.Cursor := crHourGlass;
   try
-    FOptionsThread.WaitFor;            // Make sure the options are read.
+    FOptionsThread.EndParsing;            // Make sure the options are read.
     // Parse and separate defines from other options.
     FOptionsReader.FromCustomOptions(FCustomOptions);
     // Check the found defines in the GUI.
diff --git a/ide/frames/compiler_other_options.pas b/ide/frames/compiler_other_options.pas
index 0784aa275d..bedb9d24e8 100644
--- a/ide/frames/compiler_other_options.pas
+++ b/ide/frames/compiler_other_options.pas
@@ -31,7 +31,7 @@ uses
   Classes, SysUtils, math, AVL_Tree, LazLogger, Forms, Controls, Graphics,
   Dialogs, StdCtrls, LCLProc, ComCtrls, LCLType, ExtCtrls, Buttons,
   CodeToolsCfgScript, KeywordFuncLists, LazarusIDEStrConsts,
-  IDEOptionsIntf, CompOptsIntf, IDECommands, Project, PackageDefs,
+  IDEOptionsIntf, CompOptsIntf, IDECommands, LazIDEIntf, Project, PackageDefs,
   CompilerOptions, Compiler, AllCompilerOptions, CustomDefines,
   EditorOptions, SynEdit, SynEditKeyCmds, SynCompletion, SourceSynEditor;
 
@@ -366,18 +366,15 @@ begin
   if Value then begin
     if Assigned(fOptionsThread) then
     begin
-      fOptionsThread.WaitFor;       // Make sure the thread has finished running.
+      fOptionsThread.EndParsing;       // Make sure the thread has finished running.
       if FOptionsReader.UpdateTargetParam then begin
-        // Does not happen because UpdateTargetParam uses global macros
-        //  which change only after closing the options window.
-        // This code is here for future refactoring, to react to changed target in GUI.
         FOptionsReader.Clear;
-        fOptionsThread.Start;       // Read new options.
+        fOptionsThread.StartParsing;   // Read new options.
       end;
     end
     else begin
       fOptionsThread := TCompilerOptThread.Create(FOptionsReader);
-      fOptionsThread.Start;
+      fOptionsThread.StartParsing;
     end;
   end;
 end;
@@ -391,6 +388,8 @@ end;
 
 procedure TCompilerOtherOptionsFrame.SetIdleConnected(AValue: Boolean);
 begin
+  if csDestroying in ComponentState then
+    AValue:=false;
   if FIdleConnected=AValue then exit;
   FIdleConnected:=AValue;
   if FIdleConnected then
@@ -675,6 +674,7 @@ end;
 
 destructor TCompilerOtherOptionsFrame.Destroy;
 begin
+  IdleConnected:=false;
   FreeAndNil(fOptionsThread);
   FreeAndNil(FOptionsReader);
   FreeAndNil(FCompletionHistory);