diff --git a/glanceclient/common/http.py b/glanceclient/common/http.py
index 6951939..352ba10 100644
--- a/glanceclient/common/http.py
+++ b/glanceclient/common/http.py
@@ -103,7 +103,7 @@ class _BaseHTTPClient(object):
                        'response_request_id': request_id})
 
         if not resp.ok:
-            LOG.debug("Request returned failure status %s." % resp.status_code)
+            LOG.debug("Request returned failure status %s.", resp.status_code)
             raise exc.from_response(resp, resp.content)
         elif (resp.status_code == requests.codes.MULTIPLE_CHOICES and
               resp.request.path_url != '/versions'):