diff --git a/teachings.json b/teachings.json
index d53f99b..1f89f41 100644
--- a/teachings.json
+++ b/teachings.json
@@ -219,7 +219,7 @@
   {
     "name": "Ottimizzazione combinatoria",
     "url": "ottimizzazione-combinatoria",
-    "chat": "t.me/joinchat/klw79l5tkPM1NWQ0",
+    "chat": "t.me/+44Dga6Nrfh03YzY0",
     "website": "460495",
     "professors": ["ugo.dallago"]
   },
@@ -258,7 +258,7 @@
   {
     "name": "Sistemi operativi",
     "url": "sistemi-operativi",
-    "chat": "t.me/joinchat/2hUcGLfY7Gc2MTA8",
+    "chat": "t.me/+nKtJo7UaqYA2MGZk",
     "website": "320578",
     "professors": ["renzo.davoli"]
   },