diff --git a/allauth_ens/providers/clipper/provider.py b/allauth_ens/providers/clipper/provider.py
index d14bee2..967bce3 100644
--- a/allauth_ens/providers/clipper/provider.py
+++ b/allauth_ens/providers/clipper/provider.py
@@ -21,6 +21,12 @@ class ClipperProvider(CASProvider):
         uid, extra = data
         return '{}@clipper.ens.fr'.format(uid.strip().lower())
 
+    def extract_uid(self, data):
+        # Normalize UID
+        uid, _ = data
+        uid = uid.lower().strip()
+        return uid
+        
     def extract_common_fields(self, data):
         def get_names(clipper):
             assert clipper.isalnum()