--- a/utils.py  
+++ a/utils.py  
@@ -18,7 +18,7 @@ 
 main pylint class
 """
 
-import sys
+import sys, types
 from os import linesep
 
 from logilab.common.textutils import normalize_text
@@ -181,8 +181,10 @@ class MessagesHandlerMixIn:
             self.config.enable_msg = [mid for mid, val in msgs.items() if val]
 
     def _cat_ids(self, categories):
+        if isinstance(categories, types.StringType):
+            categories = [categories]
         for catid in categories:
-            catid = catid.upper()
+            catid = catid[0].upper()
             if not catid in MSG_TYPES:
                 raise Exception('Unknown category identifier %s' % catid)
             yield catid