diff --git a/src/group_gui.cpp b/src/group_gui.cpp
--- a/src/group_gui.cpp
+++ b/src/group_gui.cpp
@@ -359,7 +359,7 @@ public:
 		*this->sorting = this->vehicles.GetListing();
 	}
 
-	virtual void UpdateWidgetSize(int widget, Dimension *size, const Dimension &padding, Dimension *fill, Dimension *resize)
+	void UpdateWidgetSize(int widget, Dimension *size, const Dimension &padding, Dimension *fill, Dimension *resize) override
 	{
 		switch (widget) {
 			case WID_GL_LIST_GROUP: {
@@ -423,7 +423,7 @@ public:
 	 * @param data Information about the changed data.
 	 * @param gui_scope Whether the call is done from GUI scope. You may not do everything when not in GUI scope. See #InvalidateWindowData() for details.
 	 */
-	virtual void OnInvalidateData(int data = 0, bool gui_scope = true)
+	void OnInvalidateData(int data = 0, bool gui_scope = true) override
 	{
 		if (data == 0) {
 			/* This needs to be done in command-scope to enforce rebuilding before resorting invalid data */
@@ -447,7 +447,7 @@ public:
 		this->SetDirty();
 	}
 
-	virtual void SetStringParameters(int widget) const
+	void SetStringParameters(int widget) const override
 	{
 		switch (widget) {
 			case WID_GL_AVAILABLE_VEHICLES:
@@ -474,7 +474,7 @@ public:
 		}
 	}
 
-	virtual void OnPaint()
+	void OnPaint() override
 	{
 		/* If we select the all vehicles, this->list will contain all vehicles of the owner
 		 * else this->list will contain all vehicles which belong to the selected group */
@@ -529,7 +529,7 @@ public:
 		this->DrawWidgets();
 	}
 
-	virtual void DrawWidget(const Rect &r, int widget) const
+	void DrawWidget(const Rect &r, int widget) const override
 	{
 		switch (widget) {
 			case WID_GL_ALL_VEHICLES:
@@ -628,7 +628,7 @@ public:
 		}
 	}
 
-	virtual void OnClick(Point pt, int widget, int click_count)
+	void OnClick(Point pt, int widget, int click_count) override
 	{
 		switch (widget) {
 			case WID_GL_SORT_BY_ORDER: // Flip sorting method ascending/descending
@@ -806,7 +806,7 @@ public:
 		}
 	}
 
-	virtual void OnDragDrop(Point pt, int widget)
+	void OnDragDrop(Point pt, int widget) override
 	{
 		if (this->vehicle_sel != INVALID_VEHICLE) OnDragDrop_Vehicle(pt, widget);
 		if (this->group_sel != INVALID_GROUP) OnDragDrop_Group(pt, widget);
@@ -814,19 +814,19 @@ public:
 		_cursor.vehchain = false;
 	}
 
-	virtual void OnQueryTextFinished(char *str)
+	void OnQueryTextFinished(char *str) override
 	{
 		if (str != NULL) DoCommandP(0, this->group_rename, 0, CMD_ALTER_GROUP | CMD_MSG(STR_ERROR_GROUP_CAN_T_RENAME), NULL, str);
 		this->group_rename = INVALID_GROUP;
 	}
 
-	virtual void OnResize()
+	void OnResize() override
 	{
 		this->group_sb->SetCapacityFromWidget(this, WID_GL_LIST_GROUP);
 		this->vscroll->SetCapacityFromWidget(this, WID_GL_LIST_VEHICLE);
 	}
 
-	virtual void OnDropdownSelect(int widget, int index)
+	void OnDropdownSelect(int widget, int index) override
 	{
 		switch (widget) {
 			case WID_GL_SORT_BY_DROPDOWN:
@@ -866,14 +866,14 @@ public:
 		this->SetDirty();
 	}
 
-	virtual void OnGameTick()
+	void OnGameTick() override
 	{
 		if (this->groups.NeedResort() || this->vehicles.NeedResort()) {
 			this->SetDirty();
 		}
 	}
 
-	virtual void OnPlaceObjectAbort()
+	void OnPlaceObjectAbort() override
 	{
 		/* abort drag & drop */
 		this->vehicle_sel = INVALID_VEHICLE;
@@ -882,7 +882,7 @@ public:
 		this->SetWidgetDirty(WID_GL_LIST_VEHICLE);
 	}
 
-	virtual void OnMouseDrag(Point pt, int widget)
+	void OnMouseDrag(Point pt, int widget) override
 	{
 		if (this->vehicle_sel == INVALID_VEHICLE && this->group_sel == INVALID_GROUP) return;