diff --git a/widget/gtk/nsNativeThemeGTK.cpp b/widget/gtk/nsNativeThemeGTK.cpp
index 25e7849fff06..004896d92595 100644
--- a/widget/gtk/nsNativeThemeGTK.cpp
+++ b/widget/gtk/nsNativeThemeGTK.cpp
@@ -1475,33 +1475,15 @@ nsNativeThemeGTK::GetMinimumWidgetSize(nsPresContext* aPresContext,
     case NS_THEME_SCROLLBAR_HORIZONTAL:
     case NS_THEME_SCROLLBAR_VERTICAL:
     {
-      /* While we enforce a minimum size for the thumb, this is ignored
-       * for the some scrollbars if buttons are hidden (bug 513006) because
-       * the thumb isn't a direct child of the scrollbar, unlike the buttons
-       * or track. So add a minimum size to the track as well to prevent a
-       * 0-width scrollbar. */
       if (gtk_check_version(3,20,0) == nullptr) {
-        // Thumb min dimensions to start with
-        WidgetNodeType thumbType = aWidgetType == NS_THEME_SCROLLBAR_VERTICAL ?
-          MOZ_GTK_SCROLLBAR_THUMB_VERTICAL : MOZ_GTK_SCROLLBAR_THUMB_HORIZONTAL;
-        int thumbMinWidth, thumbMinHeight;
-        moz_gtk_get_widget_min_size(thumbType, &(aResult->width), &(aResult->height));
-
-        // Add scrollbar's borders
-        nsIntMargin border;
-        nsNativeThemeGTK::GetWidgetBorder(aFrame->PresContext()->DeviceContext(),
-                                          aFrame, aWidgetType, &border);
-        aResult->width += border.left + border.right;
-        aResult->height += border.top + border.bottom;
-
-        // Add track's borders
-        uint8_t trackType = aWidgetType == NS_THEME_SCROLLBAR_VERTICAL ?
-          NS_THEME_SCROLLBARTRACK_VERTICAL : NS_THEME_SCROLLBARTRACK_HORIZONTAL;
-        nsNativeThemeGTK::GetWidgetBorder(aFrame->PresContext()->DeviceContext(),
-                                          aFrame, trackType, &border);
-        aResult->width += border.left + border.right;
-        aResult->height += border.top + border.bottom;
+          moz_gtk_get_widget_min_size(NativeThemeToGtkTheme(aWidgetType, aFrame),
+                                      &(aResult->width), &(aResult->height));
       } else {
+        /* While we enforce a minimum size for the thumb, this is ignored
+         * for the some scrollbars if buttons are hidden (bug 513006) because
+         * the thumb isn't a direct child of the scrollbar, unlike the buttons
+         * or track. So add a minimum size to the track as well to prevent a
+         * 0-width scrollbar. */
         MozGtkScrollbarMetrics metrics;
         moz_gtk_get_scrollbar_metrics(&metrics);