diff --git a/gestion/tools/whosthere.py b/gestion/tools/whosthere.py
index 247c91cb..5b473823 100755
--- a/gestion/tools/whosthere.py
+++ b/gestion/tools/whosthere.py
@@ -192,5 +192,6 @@ if __name__ == '__main__':
         try:
             name = where[what.lower()]
         except KeyError:
-            continue
+            print "Usage: whosthere.py <local>\n  Locaux : %s" % (", ".join(where.keys()))
+            sys.exit(1)
         name().summary()