diff --git a/pyproject.toml b/pyproject.toml
index c6f73359..4f76be36 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -65,7 +65,7 @@ dependencies = [
     "requests>=2.9.1",
     "requests-oauthlib",
     "semantic-version",
-    "slixmpp",
+    "slixmpp<1.9",
 ]
 optional-dependencies.docs = [
     "myst-parser",