diff --git a/Xwt.Gtk/Xwt.GtkBackend/BoxBackendGtk3.cs b/Xwt.Gtk/Xwt.GtkBackend/BoxBackendGtk3.cs
index ee9d62da9..c781991df 100644
--- a/Xwt.Gtk/Xwt.GtkBackend/BoxBackendGtk3.cs
+++ b/Xwt.Gtk/Xwt.GtkBackend/BoxBackendGtk3.cs
@@ -92,7 +92,7 @@ protected override void OnGetPreferredWidth (out int minimum_width, out int natu
 			// dirty fix: do not constrain height on first allocation
 			var force_height = SizeConstraint.Unconstrained;
 			if (IsReallocating)
-				force_height = SizeConstraint.WithSize (Allocation.Width);
+				force_height = SizeConstraint.WithSize (Allocation.Height);
 			var size = OnGetRequisition (SizeConstraint.Unconstrained, force_height);
 			if (size.Height < WidthRequest)
 				minimum_width = natural_width = WidthRequest;