diff --git a/auth.py b/auth.py
index 50c4eeeef..3110ab868 100644
--- a/auth.py
+++ b/auth.py
@@ -18,6 +18,7 @@ from utils import data_dir
 from utils import has_users_path
 from utils import text_in_file
 from utils import remove_eol
+from utils import valid_nickname
 from timeFunctions import date_utcnow
 
 
@@ -89,7 +90,7 @@ def create_basic_auth_header(nickname: str, password: str) -> str:
 
 
 def authorize_basic(base_dir: str, path: str, auth_header: str,
-                    debug: bool) -> bool:
+                    debug: bool, domain: str) -> bool:
     """HTTP basic auth
     """
     if ' ' not in auth_header:
@@ -140,6 +141,10 @@ def authorize_basic(base_dir: str, path: str, auth_header: str,
                   ') does not match the one in the Authorization header (' +
                   nickname + ')')
         return False
+    if not valid_nickname(domain, nickname):
+        if debug:
+            print('AUTH: invalid nickname ' + nickname)
+        return False
     if is_memorial_account(base_dir, nickname):
         print('basic auth - attempted login using memorial account ' +
               nickname + ' in Auth header')
@@ -248,11 +253,12 @@ def remove_password(base_dir: str, nickname: str) -> None:
             return
 
 
-def authorize(base_dir: str, path: str, auth_header: str, debug: bool) -> bool:
+def authorize(base_dir: str, path: str, auth_header: str, debug: bool,
+              domain: str) -> bool:
     """Authorize using http header
     """
     if auth_header.lower().startswith('basic '):
-        return authorize_basic(base_dir, path, auth_header, debug)
+        return authorize_basic(base_dir, path, auth_header, debug, domain)
     return False
 
 
diff --git a/daemon_post_login.py b/daemon_post_login.py
index 9a15fb578..92cf740af 100644
--- a/daemon_post_login.py
+++ b/daemon_post_login.py
@@ -141,7 +141,8 @@ def post_login_screen(self, calling_domain: str, cookie: str,
                 print('Login attempt from IP: ' + str(ip_address))
         if not authorize_basic(base_dir, '/users/' +
                                login_nickname + '/outbox',
-                               auth_header, False):
+                               auth_header, False,
+                               domain):
             print('Login failed: ' + login_nickname)
             clear_login_details(self, login_nickname, calling_domain)
             fail_time = int(time.time())
diff --git a/daemon_utils.py b/daemon_utils.py
index 1f6685697..d935072a4 100644
--- a/daemon_utils.py
+++ b/daemon_utils.py
@@ -626,7 +626,8 @@ def is_authorized(self) -> bool:
     if self.headers.get('Authorization'):
         if authorize(self.server.base_dir, self.path,
                      self.headers['Authorization'],
-                     self.server.debug):
+                     self.server.debug,
+                     self.server.domain):
             return True
         print('AUTH: C2S Basic auth did not authorize ' +
               self.headers['Authorization'])
diff --git a/tests.py b/tests.py
index 100314a03..da405f63c 100644
--- a/tests.py
+++ b/tests.py
@@ -3277,24 +3277,25 @@ def _test_authentication(base_dir: str) -> None:
     assert store_basic_credentials(base_dir, 'badnick', 'otherpa:ss') is False
     assert store_basic_credentials(base_dir, nickname, password)
 
+    domain = "test.domain"
     auth_header = create_basic_auth_header(nickname, password)
     assert authorize_basic(base_dir, '/users/' + nickname + '/inbox',
-                           auth_header, False)
+                           auth_header, False, domain)
     assert authorize_basic(base_dir, '/users/' + nickname,
-                           auth_header, False) is False
+                           auth_header, False, domain) is False
     assert authorize_basic(base_dir, '/users/othernick/inbox',
-                           auth_header, False) is False
+                           auth_header, False, domain) is False
 
     auth_header = create_basic_auth_header(nickname, password + '1')
     assert authorize_basic(base_dir, '/users/' + nickname + '/inbox',
-                           auth_header, False) is False
+                           auth_header, False, domain) is False
 
     password = 'someOtherPassword'
     assert store_basic_credentials(base_dir, nickname, password)
 
     auth_header = create_basic_auth_header(nickname, password)
     assert authorize_basic(base_dir, '/users/' + nickname + '/inbox',
-                           auth_header, False)
+                           auth_header, False, domain)
 
     os.chdir(curr_dir)
     shutil.rmtree(base_dir, ignore_errors=False)