diff --git a/lcl/interfaces/gtk3/gtk3widgets.pas b/lcl/interfaces/gtk3/gtk3widgets.pas
index 849c6141d1..947f9f9e8f 100644
--- a/lcl/interfaces/gtk3/gtk3widgets.pas
+++ b/lcl/interfaces/gtk3/gtk3widgets.pas
@@ -634,6 +634,7 @@ type
     function CreateWidget(const Params: TCreateParams):PGtkWidget; override;
   public
     function IsWidgetOk: Boolean; override;
+    procedure SetDefault(const ADefault: Boolean);
     property Layout: Integer read getLayout write SetLayout;
     property Margin: Integer read getMargin write SetMargin;
     property Spacing: Integer read FSpacing write SetSpacing;
@@ -5742,6 +5743,12 @@ begin
   Result := (FWidget <> nil) and Gtk3IsButton(FWidget);
 end;
 
+procedure TGtk3Button.SetDefault(const ADefault: Boolean);
+begin
+  if IsWidgetOk then
+    GetContainerWidget^.set_can_default(ADefault);
+end;
+
 { TGtk3ToggleButton }
 procedure Gtk3Toggled(AWidget: PGtkToggleButton; AData: gPointer); cdecl;
 var
diff --git a/lcl/interfaces/gtk3/gtk3wsstdctrls.pp b/lcl/interfaces/gtk3/gtk3wsstdctrls.pp
index 4453faea4d..5ace11c717 100644
--- a/lcl/interfaces/gtk3/gtk3wsstdctrls.pp
+++ b/lcl/interfaces/gtk3/gtk3wsstdctrls.pp
@@ -1045,7 +1045,9 @@ end;
 
 class procedure TGtk3WSButton.SetDefault(const AButton: TCustomButton; ADefault: Boolean);
 begin
-  //TODO:
+  if not WSCheckHandleAllocated(AButton, 'SetDefault') then
+    Exit;
+  TGtk3Button(AButton.Handle).SetDefault(ADefault);
 end;
 
 class procedure TGtk3WSButton.SetShortCut(const AButton: TCustomButton;