diff --git a/lcl/interfaces/qt5/qtwidgets.pas b/lcl/interfaces/qt5/qtwidgets.pas
index 086e2515b6..019958fec8 100644
--- a/lcl/interfaces/qt5/qtwidgets.pas
+++ b/lcl/interfaces/qt5/qtwidgets.pas
@@ -28,7 +28,7 @@ uses
   // Free Pascal
   Classes, SysUtils, Types,
   // LCL
-  LCLType, LCLProc, LazUTF8, LCLIntf, LMessages, Graphics, Forms, Controls,
+  LCLType, LCLProc, LazUTF8, LazStringUtils, LCLIntf, LMessages, Graphics, Forms, Controls,
   ComCtrls, ExtCtrls, StdCtrls, Menus, Dialogs, ImgList;
 
 type
@@ -19293,16 +19293,34 @@ end;
 procedure TQtFileDialog.FilterSelectedEvent(filter: PWideString); cdecl;
 var
   List: TQtStringList;
-  index: Integer;
+  i, index: Integer;
+  s: String;
 begin
   if filter <> nil then
   begin
     List := TQtStringList.Create;
-    getFilters(List.Handle);
-    index := List.IndexOf(UTF16ToUTF8(filter^));
-    if index <> -1 then
-      TFileDialog(FDialog).IntfFileTypeChanged(index + 1);
-    List.Free;
+    try
+      getFilters(List.Handle);
+      s := UTF16ToUTF8(filter^);
+      index := -1;
+      if s <> '' then
+        if s[Length(s)] = ')' then // if QFileDialogDontUseNativeDialog = True
+          index := List.IndexOf(s)
+        else
+        begin
+          s := '(' + s + ')';
+          for i := 0 to List.Count - 1 do
+            if LazEndsStr(s, List[i]) then
+            begin
+              index := i;
+              break;
+            end;
+        end;
+      if index <> -1 then
+        TFileDialog(FDialog).IntfFileTypeChanged(index + 1);
+    finally
+      List.Free;
+    end;
   end;
 end;
 
diff --git a/lcl/interfaces/qt5/qtwsdialogs.pp b/lcl/interfaces/qt5/qtwsdialogs.pp
index cd6e939bd7..a64308b52f 100644
--- a/lcl/interfaces/qt5/qtwsdialogs.pp
+++ b/lcl/interfaces/qt5/qtwsdialogs.pp
@@ -189,15 +189,24 @@ end;
 class function TQtWSFileDialog.GetQtFilterString(const AFileDialog: TFileDialog;
   var ASelectedFilter: WideString): WideString;
 
-  function GetExtensionString(ASource: String; AStart, ALength: Integer): String; inline;
+const
+  FULLWIDTH_LEFT_PARENTHESIS_UTF8 = #$EF#$BC#$88;
+  FULLWIDTH_RIGHT_PARENTHESIS_UTF8 = #$EF#$BC#$89;
+
+  function ReplaceExtensionDelimiter(const ASource: String): String; inline;
   begin
-    // replace *.ext1, *.ext2 by *.ext1 *.ext2
-    Result := '(' + StringReplace(Copy(ASource, AStart, ALength), ';', ' ', [rfReplaceAll]) + ')';
+    // replace *.ext1;*.ext2 by *.ext1 *.ext2
+    Result := StringReplace(ASource, ';', ' ', [rfReplaceAll]);
+  end;
+
+  function GetExtensionString(const ASource: String): String; inline;
+  begin
+    Result := '(' + ReplaceExtensionDelimiter(ASource) + ')';
   end;
   
 var
-  TmpFilter, strExtensions, DialogFilter: string;
-  ParserState, Position, i: Integer;
+  TmpFilter, strExtensions, DialogFilter, S, S1: string;
+  ParserState, Position, i, L: Integer;
   List: TStrings;
 begin
     {------------------------------------------------------------------------------
@@ -231,61 +240,47 @@ begin
   ParserState := 0;
   Position := 1;
   TmpFilter := AFileDialog.Filter;
-  DialogFilter := AFileDialog.Filter;
   ASelectedFilter := '';
 
-  {we must remove all brackets since qt-45 doesn't like brackets
-   outside filters,so our eg. Pascal source (*.pas;*.pp) | *.pas;*.pp
-   becomes invalid after filters processing.}
-  TmpFilter := StringReplace(TmpFilter,'(','',[rfReplaceAll]);
-  TmpFilter := StringReplace(TmpFilter,')','',[rfReplaceAll]);
   DialogFilter := TmpFilter;
 
   TmpFilter := '';
 
   List := TStringList.Create;
   try
-    for i := 1 to Length(DialogFilter) do
+    S1 := '';
+    L := Length(DialogFilter);
+    for i := 1 to L + 1 do
     begin
-      if Copy(DialogFilter, i, 1) = '|' then
+      if (i = L + 1) or (DialogFilter[i] = '|') then
       begin
         ParserState := ParserState + 1;
 
+        S := Copy(DialogFilter, Position, i - Position);
         if ParserState = 1 then
         begin
-          List.Add(Copy(DialogFilter, Position, i - Position));
-          TmpFilter := TmpFilter + Copy(DialogFilter, Position, i - Position);
+          S := StringReplace(S, ' (', FULLWIDTH_LEFT_PARENTHESIS_UTF8, []);
+          S := StringReplace(S, '(', FULLWIDTH_LEFT_PARENTHESIS_UTF8, []);
+          S := StringReplace(S, ')', FULLWIDTH_RIGHT_PARENTHESIS_UTF8, []);
+          S1 := S;
+          List.Add(S1);
+          TmpFilter := TmpFilter + S1;
         end else
-        if ParserState = 2 then
+        //if ParserState = 2 then
         begin
-          strExtensions := GetExtensionString(DialogFilter, Position, i - Position);
-
-          if Pos(strExtensions, TmpFilter) = 0 then
-          begin
-            if List.Count > 0 then
-              List.Strings[List.Count - 1] := List.Strings[List.Count - 1] +' '+ strExtensions;
-            TmpFilter := TmpFilter + ' ' + strExtensions;
-          end;
-
-          TmpFilter := TmpFilter + ';;';
+          strExtensions := GetExtensionString(S);
+          List.Strings[List.Count - 1] := S1 + ' ' + strExtensions;
+          TmpFilter := TmpFilter + ' ' + strExtensions;
 
+          if i <> L + 1 then
+            TmpFilter := TmpFilter + ';;';
           ParserState := 0;
         end;
 
-        if i <> Length(DialogFilter) then
-          Position := i + 1;
+        Position := i + 1;
       end;
     end;
 
-    strExtensions := GetExtensionString(DialogFilter, Position, i + 1 - Position);
-
-    if Pos(strExtensions, TmpFilter) = 0 then
-    begin
-      if List.Count > 0 then
-        List.Strings[List.Count - 1] := List.Strings[List.Count - 1] +' '+ strExtensions;
-      TmpFilter := TmpFilter + ' ' + strExtensions;
-    end;
-
     // Remember that AFileDialog.FilterIndex is a 1-based index and that
     // List has a zero-based index
     if (AFileDialog.FilterIndex > 0) and (List.Count >= AFileDialog.FilterIndex) then