diff --git a/kolabd/__init__.py b/kolabd/__init__.py
--- a/kolabd/__init__.py
+++ b/kolabd/__init__.py
@@ -289,8 +289,8 @@
                     level=8
                 )
 
-                domain_root_dns[primary] = domain_root_dn
-                naming_contexts[primary] = naming_context
+                domain_root_dns[primary] = domain_root_dn.lower()
+                naming_contexts[primary] = naming_context.lower()
 
             log.debug(
                 _l("Naming contexts to synchronize: %r") % (
diff --git a/pykolab/auth/ldap/__init__.py b/pykolab/auth/ldap/__init__.py
--- a/pykolab/auth/ldap/__init__.py
+++ b/pykolab/auth/ldap/__init__.py
@@ -2378,7 +2378,7 @@
 
         # If we have a 1:1 match, continue as planned
         for naming_context in naming_contexts:
-            if self.domain_rootdns[domain].endswith(naming_context):
+            if self.domain_rootdns[domain].lower().endswith(naming_context):
                 return naming_context
 
     def _primary_domain_for_naming_context(self, naming_context):