diff --git a/data/gui/macros/_initial.cfg b/data/gui/macros/_initial.cfg
index 3ca6d24586f0..d5837a7127ad 100644
--- a/data/gui/macros/_initial.cfg
+++ b/data/gui/macros/_initial.cfg
@@ -222,6 +222,24 @@
 	[/stacked_widget]
 #enddef
 
+# Forces a widget to be of a certain size and blocks it from growing.
+#
+# WIDTH                      Width for the widget.
+# HEIGHT                     Height for the widget.
+# WIDGET                     The widget to add to the item.
+#
+#define GUI_FORCE_WIDGET_SIZE WIDTH HEIGHT WIDGET
+	[size_lock]
+		definition = "default"
+		width = "{WIDTH}"
+		height = "{HEIGHT}"
+
+		[widget]
+			{WIDGET}
+		[/widget]
+	[/size_lock]
+#enddef
+
 #define GUI_WINDOW_FULLSCREEN
 	automatic_placement = false
 	x = 0
diff --git a/data/gui/window/lobby_main.cfg b/data/gui/window/lobby_main.cfg
index f3d61f0affdb..7aa2bf743ed2 100644
--- a/data/gui/window/lobby_main.cfg
+++ b/data/gui/window/lobby_main.cfg
@@ -764,35 +764,35 @@
 					horizontal_grow = true
 					vertical_grow = true
 
-					[grid]
-						fixed_height = "((screen_height * 20) / 100)"
-
-						[row]
-							grow_factor = 1
-
-							[column]
+					{GUI_FORCE_WIDGET_SIZE 0 "((screen_height * 20) / 100)" (
+						[grid]
+							[row]
 								grow_factor = 1
-								horizontal_grow = true
-								vertical_grow = true
 
-								[chatbox]
-									id = "chat"
-								[/chatbox]
-							[/column]
+								[column]
+									grow_factor = 1
+									horizontal_grow = true
+									vertical_grow = true
 
-							[column]
-								grow_factor = 0
-								border = "top"
-								border_size = 5
-								horizontal_grow = true
-								vertical_grow = true
+									[chatbox]
+										id = "chat"
+									[/chatbox]
+								[/column]
 
-								[grid]
-									{_GUI_PLAYER_TREE_AREA}
-								[/grid]
-							[/column]
-						[/row]
-					[/grid]
+								[column]
+									grow_factor = 0
+									border = "top"
+									border_size = 5
+									horizontal_grow = true
+									vertical_grow = true
+
+									[grid]
+										{_GUI_PLAYER_TREE_AREA}
+									[/grid]
+								[/column]
+							[/row]
+						[/grid]
+					)}
 				[/column]
 			[/row]
 		[/grid]
@@ -883,10 +883,11 @@
 											horizontal_grow = true
 											vertical_grow = true
 
-											[chatbox]
-												id = "chat"
-												fixed_height = "((screen_height * 25 / 100))"
-											[/chatbox]
+											{GUI_FORCE_WIDGET_SIZE 0 "((screen_height * 25 / 100))" (
+												[chatbox]
+													id = "chat"
+												[/chatbox]
+											)}
 										[/column]
 									[/row]
 								[/grid]
diff --git a/data/gui/window/mp_join_game.cfg b/data/gui/window/mp_join_game.cfg
index 000dd480260e..a5190df24378 100644
--- a/data/gui/window/mp_join_game.cfg
+++ b/data/gui/window/mp_join_game.cfg
@@ -411,7 +411,7 @@
 				# This is exactly the size of two large-sized buttons (116 x 2) plus the interior
 				# border space between them (10). It keeps this column the same size as the corresponding
 				# one in MP Staging, which has the above layout (2 buttons, etc).
-				{GUI_FORCE_WIDGET_MINIMUM_SIZE 242 0 (
+				{GUI_FORCE_WIDGET_MINIMUM_SIZE 242 0 ( 
 					[button]
 						id = "cancel"
 						definition = "large"
@@ -558,10 +558,11 @@
 											horizontal_grow = true
 											vertical_grow = true
 
-											[chatbox]
-												id = "chat"
-												fixed_height = "((screen_height * 25 / 100))"
-											[/chatbox]
+											{GUI_FORCE_WIDGET_SIZE 0 "((screen_height * 25 / 100))" (
+												[chatbox]
+													id = "chat"
+												[/chatbox]
+											)}
 										[/column]
 
 									[/row]
diff --git a/data/gui/window/mp_staging.cfg b/data/gui/window/mp_staging.cfg
index 9e4d34dcf443..127629172593 100644
--- a/data/gui/window/mp_staging.cfg
+++ b/data/gui/window/mp_staging.cfg
@@ -707,10 +707,11 @@
 								horizontal_grow = true
 								vertical_grow = true
 
-								[chatbox]
-									id = "chat"
-									fixed_height = "((screen_height * 25 / 100))"
-								[/chatbox]
+								{GUI_FORCE_WIDGET_SIZE 0 "((screen_height * 25 / 100))" (
+									[chatbox]
+										id = "chat"
+									[/chatbox]
+								)}
 							[/column]
 
 							[column]
@@ -881,10 +882,11 @@
 											horizontal_grow = true
 											vertical_grow = true
 
-											[chatbox]
-												id = "chat"
-												fixed_height = "((screen_height * 25 / 100))"
-											[/chatbox]
+											{GUI_FORCE_WIDGET_SIZE 0 "((screen_height * 25 / 100))" (
+												[chatbox]
+													id = "chat"
+												[/chatbox]
+											)}
 										[/column]
 
 									[/row]