diff -Nrup a/gajim/common/app.py b/gajim/common/app.py
--- a/gajim/common/app.py	2023-01-07 16:21:49.000000000 +0100
+++ b/gajim/common/app.py	2023-05-24 21:28:47.782144228 +0200
@@ -187,6 +187,7 @@ def detect_dependencies() -> None:
     try:
         gi.require_version('Gst', '1.0')
         gi.require_version('GstPbutils', '1.0')
+        gi.require_version('GtkSource', '4')
         from gi.repository import Gst
         from gi.repository import GstPbutils  # noqa: F401
         success, _argv = Gst.init_check(None)