diff --git a/gtk/gtkcssnode.c b/gtk/gtkcssnode.c
index e61497181d..ddb7f0f978 100644
--- a/gtk/gtkcssnode.c
+++ b/gtk/gtkcssnode.c
@@ -1203,7 +1203,7 @@ gtk_css_node_get_classes (GtkCssNode *cssnode)
   return result;
 }
 
-void
+gboolean
 gtk_css_node_add_class (GtkCssNode *cssnode,
                         GQuark      style_class)
 {
@@ -1211,10 +1211,13 @@ gtk_css_node_add_class (GtkCssNode *cssnode,
     {
       gtk_css_node_invalidate (cssnode, GTK_CSS_CHANGE_CLASS);
       g_object_notify_by_pspec (G_OBJECT (cssnode), cssnode_properties[PROP_CLASSES]);
+      return TRUE;
     }
+
+  return FALSE;
 }
 
-void
+gboolean
 gtk_css_node_remove_class (GtkCssNode *cssnode,
                            GQuark      style_class)
 {
@@ -1222,7 +1225,10 @@ gtk_css_node_remove_class (GtkCssNode *cssnode,
     {
       gtk_css_node_invalidate (cssnode, GTK_CSS_CHANGE_CLASS);
       g_object_notify_by_pspec (G_OBJECT (cssnode), cssnode_properties[PROP_CLASSES]);
+      return TRUE;
     }
+
+  return FALSE;
 }
 
 gboolean
diff --git a/gtk/gtkcssnodeprivate.h b/gtk/gtkcssnodeprivate.h
index 59f4dcd504..98c4611c3a 100644
--- a/gtk/gtkcssnodeprivate.h
+++ b/gtk/gtkcssnodeprivate.h
@@ -128,9 +128,9 @@ GtkStateFlags           gtk_css_node_get_state          (GtkCssNode            *
 void                    gtk_css_node_set_classes        (GtkCssNode            *cssnode,
                                                          const char           **classes);
 char **                 gtk_css_node_get_classes        (GtkCssNode            *cssnode);
-void                    gtk_css_node_add_class          (GtkCssNode            *cssnode,
+gboolean                gtk_css_node_add_class          (GtkCssNode            *cssnode,
                                                          GQuark                 style_class);
-void                    gtk_css_node_remove_class       (GtkCssNode            *cssnode,
+gboolean                gtk_css_node_remove_class       (GtkCssNode            *cssnode,
                                                          GQuark                 style_class);
 gboolean                gtk_css_node_has_class          (GtkCssNode            *cssnode,
                                                          GQuark                 style_class) G_GNUC_PURE;
diff --git a/gtk/gtkwidget.c b/gtk/gtkwidget.c
index 0219a781c6..e40d9aa3c5 100644
--- a/gtk/gtkwidget.c
+++ b/gtk/gtkwidget.c
@@ -13053,8 +13053,8 @@ gtk_widget_add_css_class (GtkWidget  *widget,
   g_return_if_fail (css_class[0] != '\0');
   g_return_if_fail (css_class[0] != '.');
 
-  gtk_css_node_add_class (priv->cssnode, g_quark_from_string (css_class));
-  g_object_notify_by_pspec (G_OBJECT (widget), widget_props[PROP_CSS_CLASSES]);
+  if (gtk_css_node_add_class (priv->cssnode, g_quark_from_string (css_class)))
+    g_object_notify_by_pspec (G_OBJECT (widget), widget_props[PROP_CSS_CLASSES]);
 }
 
 /**
@@ -13083,8 +13083,8 @@ gtk_widget_remove_css_class (GtkWidget  *widget,
   if (!class_quark)
     return;
 
-  gtk_css_node_remove_class (priv->cssnode, class_quark);
-  g_object_notify_by_pspec (G_OBJECT (widget), widget_props[PROP_CSS_CLASSES]);
+  if (gtk_css_node_remove_class (priv->cssnode, class_quark))
+    g_object_notify_by_pspec (G_OBJECT (widget), widget_props[PROP_CSS_CLASSES]);
 }
 
 /**