diff --git a/converter/convertdelphi.pas b/converter/convertdelphi.pas
index 6d41f46ef9..ef9f28c40b 100644
--- a/converter/convertdelphi.pas
+++ b/converter/convertdelphi.pas
@@ -146,6 +146,7 @@ type
     // Units that are found and will be added to project and converted.
     fUnitsToAddToProject: TStringList;
     fSettings: TConvertSettings;
+    fUseThreads: boolean;              // The project/package uses TThread.
     function ConvertSub: TModalResult;
     procedure CleanUpCompilerOptionsSearchPaths(Options: TBaseCompilerOptions);
     procedure SetCompilerModeForDefineTempl(DefTempl: TDefineTemplate);
@@ -464,6 +465,7 @@ end;
 
 destructor TConvertDelphiUnit.Destroy;
 begin
+  fUsedUnitsTool.Free;
   fCTLink.Free;
   if fOwnerConverter=nil then
     fSettings.Free;
@@ -676,7 +678,6 @@ begin
   if Assigned(fUsedUnitsTool) then begin
     Result:=fUsedUnitsTool.Convert;
     if Result<>mrOk then exit;
-    FreeAndNil(fUsedUnitsTool);
   end;
   Result:=mrOk;
 end;
@@ -782,6 +783,7 @@ constructor TConvertDelphiPBase.Create(const AFilename, ADescription: string);
 begin
   fOrigPFilename:=AFilename;
   fIsConsoleApp:=False;                      // Default = GUI app.
+  fUseThreads:=True;     // For testing.
   fUnitSearchPaths:=TStringList.Create;
   fUnitSearchPaths.Delimiter:=';';
   fUnitSearchPaths.StrictDelimiter:=True;
@@ -1463,8 +1465,13 @@ begin
       Result:=ConvertOne(CurUnitInfo);
       if Result<>mrOK then Break;
     end;
-    if Result=mrOK then
+    if Result=mrOK then begin
+      if fUseThreads then begin
+        Result:=fMainUnitConverter.fUsedUnitsTool.AddThreadSupport;
+        if Result<>mrOK then exit;
+      end;
       Result:=ConvertAllFormFiles(ConvUnits);
+    end;
   finally
     ConvUnits.Free;  // Owns and frees converter objects.
   end;
diff --git a/converter/usedunits.pas b/converter/usedunits.pas
index 62a972599f..63ceffa8d8 100644
--- a/converter/usedunits.pas
+++ b/converter/usedunits.pas
@@ -121,6 +121,7 @@ type
     function Convert: TModalResult;
     procedure MoveMissingToComment(AAllCommentedUnits: TStrings);
     procedure AddUnitIfNeeded(AUnitName: string);
+    function AddThreadSupport: TModalResult;
   public
     property MainUsedUnits: TUsedUnits read fMainUsedUnits;
     property ImplUsedUnits: TUsedUnits read fImplUsedUnits;
@@ -629,6 +630,25 @@ begin
   end;
 end;
 
+function TUsedUnitsTool.AddThreadSupport: TModalResult;
+// AddUnitToSpecificUsesSection would insert cthreads in the beginning automatically
+// It doesn't work with {$IFDEF UNIX} directive -> use UsesInsertPolicy.
+var
+  OldPolicy: TUsesInsertPolicy;
+begin
+  Result:=mrCancel;
+  with fCTLink do
+  try
+    OldPolicy:=SrcCache.BeautifyCodeOptions.UsesInsertPolicy;
+    SrcCache.BeautifyCodeOptions.UsesInsertPolicy:=uipFirst;
+    if not CodeTool.AddUnitToSpecificUsesSection(fMainUsedUnits.fUsesSection,
+                         '{$IFDEF UNIX}cthreads{$ENDIF}', '', SrcCache) then exit;
+  finally
+    SrcCache.BeautifyCodeOptions.UsesInsertPolicy:=OldPolicy;
+  end;
+  Result:=mrOK;
+end;
+
 function TUsedUnitsTool.GetMissingUnitCount: integer;
 begin
   Result:=fMainUsedUnits.fMissingUnits.Count+fImplUsedUnits.fMissingUnits.Count;