diff --git a/gtk/gtkthemingengine.c b/gtk/gtkthemingengine.c
index 3f3751284b..1d3bc129f5 100644
--- a/gtk/gtkthemingengine.c
+++ b/gtk/gtkthemingengine.c
@@ -1828,7 +1828,7 @@ render_frame_internal (GtkThemingEngine *engine,
       int offset;
 
       border_style[1] = border_style[2] = border_style[3] = border_style[0];
-      border.top = _gtk_css_value_get_int (_gtk_theming_engine_peek_property (engine, GTK_CSS_PROPERTY_OUTLINE_WIDTH));
+      border.top = round (_gtk_css_number_value_get (_gtk_theming_engine_peek_property (engine, GTK_CSS_PROPERTY_OUTLINE_WIDTH), 100));
       border.left = border.right = border.bottom = border.top;
       colors[0] = *_gtk_css_rgba_value_get_rgba (_gtk_theming_engine_peek_property (engine, GTK_CSS_PROPERTY_OUTLINE_COLOR));
       colors[3] = colors[2] = colors[1] = colors[0];