diff --git a/src/gfxinit.cpp b/src/gfxinit.cpp
--- a/src/gfxinit.cpp
+++ b/src/gfxinit.cpp
@@ -311,6 +311,7 @@
 	GfxInitPalettes();
 
 	UpdateCursorSize();
+	NWidgetLeaf::InvalidateDimensionCache();
 }
 
 bool GraphicsSet::FillSetDetails(IniFile *ini, const char *path, const char *full_filename)
diff --git a/src/widget.cpp b/src/widget.cpp
--- a/src/widget.cpp
+++ b/src/widget.cpp
@@ -2075,6 +2075,7 @@
 	resizebox_dimension.width = resizebox_dimension.height = 0;
 	closebox_dimension.width  = closebox_dimension.height  = 0;
 	dropdown_dimension.width  = dropdown_dimension.height  = 0;
+	defsizebox_dimension.width = defsizebox_dimension.height = 0;
 }
 
 Dimension NWidgetLeaf::shadebox_dimension  = {0, 0};