diff --git a/src/Previewer/Internal.js b/src/Previewer/Internal.js
index 618461d19..b61397c03 100644
--- a/src/Previewer/Internal.js
+++ b/src/Previewer/Internal.js
@@ -157,6 +157,13 @@ export default function Internal({
           object_root[prop_name] = new_value;
         }
       }
+
+      // Toplevel windows returned by these functions will stay around
+      // until the user explicitly destroys them with gtk_window_destroy().
+      // https://docs.gtk.org/gtk4/class.Builder.html
+      if (object_preview instanceof Gtk.Window) {
+        object_preview.destroy();
+      }
     }
 
     if (!object_root.name) {
diff --git a/src/Previewer/previewer.vala b/src/Previewer/previewer.vala
index 31794c269..cd6d32264 100644
--- a/src/Previewer/previewer.vala
+++ b/src/Previewer/previewer.vala
@@ -42,7 +42,7 @@ namespace Workbench {
       var target = this.builder.get_object (target_id) as Gtk.Widget;
       if (target == null) {
         stderr.printf (@"Widget with target_id='$target_id' could not be found.\n");
-          return;
+        return;
       }
 
       if (original_id != "") {
@@ -75,6 +75,13 @@ namespace Workbench {
         ((Gtk.Window) target).child = null;
         this.window.child = child;
       }
+
+      // Toplevel windows returned by these functions will stay around
+      // until the user explicitly destroys them with gtk_window_destroy().
+      // https://docs.gtk.org/gtk4/class.Builder.html
+      if (target is Gtk.Window) {
+        ((Gtk.Window) target).destroy();
+      }
     }
 
     public void update_css (string content) {