diff --git a/weboob/backends/gazelle/backend.py b/weboob/backends/gazelle/backend.py
index f7ff40bc..608be60e 100644
--- a/weboob/backends/gazelle/backend.py
+++ b/weboob/backends/gazelle/backend.py
@@ -37,7 +37,7 @@ class GazelleBackend(BaseBackend, ICapTorrent):
 
     CONFIG = {'username':      BaseBackend.ConfigField(description='Username on website'),
               'password':      BaseBackend.ConfigField(description='Password of account', is_masked=True),
-              'protocol':      BaseBackend.ConfigField(description='Protocol to use ("http" or "https")'),
+              'protocol':      BaseBackend.ConfigField(description='Protocol to use ("http" or "https")', regexp='^(http|https)$'),
               'domain':        BaseBackend.ConfigField(description='Domain (example "ssl.what.cd")'),
              }
     BROWSER = GazelleBrowser