diff --git a/lcl/interfaces/cocoa/cocoa_extra.pas b/lcl/interfaces/cocoa/cocoa_extra.pas
index 838366e6a5..ea08abc9dd 100644
--- a/lcl/interfaces/cocoa/cocoa_extra.pas
+++ b/lcl/interfaces/cocoa/cocoa_extra.pas
@@ -248,6 +248,7 @@ const
   NSAppKitVersionNumber10_13 = 1561;
   //NSAppKitVersionNumber10_14 = 1641.10; // Mojave's beta?
   NSAppKitVersionNumber10_14 = 1671;
+  NSAppKitVersionNumber11_0  = 2022; // 2000 starts with beta?
 
 
 
diff --git a/lcl/interfaces/cocoa/cocoawsdialogs.pas b/lcl/interfaces/cocoa/cocoawsdialogs.pas
index 4b887971ca..27d23861a9 100644
--- a/lcl/interfaces/cocoa/cocoawsdialogs.pas
+++ b/lcl/interfaces/cocoa/cocoawsdialogs.pas
@@ -291,7 +291,12 @@ var
     lDialogView := NSView(ASaveOwner.contentView);
     if lDialogView <> nil then
     begin
-      if lDialogView.frame.size.width > INT_MIN_ACCESSORYVIEW_WIDTH then
+      if (NSAppkitVersionNumber >= NSAppKitVersionNumber11_0) then
+        // starting with Big Sur, the dialog retains the last openned size
+        // causing the width to be increased on every openning of the dialog
+        // we'd simply force the lAccessoryWidth to start with the minimum width
+        lAccessoryWidth := INT_MIN_ACCESSORYVIEW_WIDTH
+      else if lDialogView.frame.size.width > INT_MIN_ACCESSORYVIEW_WIDTH then
         lAccessoryWidth := Round(lDialogView.frame.size.width);
     end;
     lRect := GetNSRect(0, 0, lAccessoryWidth, 30);