diff --git a/src/Library/demos/Menu Button/main.py b/src/Library/demos/Menu Button/main.py
index fa8894d2f..09a07a27d 100644
--- a/src/Library/demos/Menu Button/main.py	
+++ b/src/Library/demos/Menu Button/main.py	
@@ -17,4 +17,3 @@ def update_css(_widget, _params):
 
 
 circular_switch.connect("notify::active", update_css)
-
diff --git a/src/Library/demos/Popovers/main.py b/src/Library/demos/Popovers/main.py
index 599accb72..c2f5d1042 100644
--- a/src/Library/demos/Popovers/main.py
+++ b/src/Library/demos/Popovers/main.py
@@ -5,7 +5,7 @@
 import workbench
 
 
-def onClosed(popover):
+def on_closed(popover):
     name = popover.get_name()
     print(f"{name} closed.")
 
@@ -14,4 +14,4 @@ def onClosed(popover):
 
 for id in popover_ids:
     popover = workbench.builder.get_object(id)
-    popover.connect("closed", onClosed)
+    popover.connect("closed", on_closed)
diff --git a/src/langs/python/python-previewer.py b/src/langs/python/python-previewer.py
index 70a732de6..ddfc499ce 100644
--- a/src/langs/python/python-previewer.py
+++ b/src/langs/python/python-previewer.py
@@ -23,10 +23,14 @@
 gi.require_version("Adw", "1")
 gi.require_version("Graphene", "1.0")
 gi.require_version("Gsk", "4.0")
+gi.require_version("GtkSource", "5")
 
-from gi.repository import GLib, Gdk, Gtk, Adw, Graphene, Gio, Gsk
+from gi.repository import GLib, Gdk, Gtk, Adw, Graphene, Gio, Gsk, GtkSource
 from gi.repository.Gio import DBusConnection, DBusConnectionFlags
 
+# Load non-GTK widget types
+GtkSource.init()
+
 
 # Table of Contents
 # =================