diff --git a/spinnman/spalloc/session.py b/spinnman/spalloc/session.py
index 12b5b2a48..63c892969 100644
--- a/spinnman/spalloc/session.py
+++ b/spinnman/spalloc/session.py
@@ -238,10 +238,13 @@ def renew(self) -> JsonObject:
                          self.__login_form_url, r.status_code)
             m = csrf_matcher.search(r.text)
             if not m:
-                raise SpallocException(
-                    "Could not establish temporary session to "
-                    f"{self._service_url} for user {self.__username} "
-                    f"with a {len(self.__password)} character password.")
+                msg = ("Could not establish temporary session to "
+                       f"{self._service_url} for user {self.__username} ")
+                if self.__password is None:
+                    msg += "with a no password"
+                else:
+                    msg += f"with a {len(self.__password)} character password."
+                raise SpallocException(msg)
             csrf = m.group(1)
             session = r.cookies[_SESSION_COOKIE]