diff --git a/src/calibre/srv/tests/auth.py b/src/calibre/srv/tests/auth.py
index 34652436a7..3580862472 100644
--- a/src/calibre/srv/tests/auth.py
+++ b/src/calibre/srv/tests/auth.py
@@ -10,6 +10,7 @@ import subprocess
 import time
 from collections import namedtuple
 
+from calibre.constants import ismacos
 from calibre.ptempfile import TemporaryDirectory
 from calibre.srv.errors import HTTPForbidden
 from calibre.srv.routes import Router, endpoint
@@ -21,6 +22,7 @@ from polyglot.http_cookie import CookieJar
 from polyglot.urllib import HTTPBasicAuthHandler, HTTPCookieProcessor, HTTPDigestAuthHandler, HTTPError, build_opener
 
 REALM = 'calibre-test'
+is_ci = os.environ.get('CI', '').lower() == 'true'
 
 
 @endpoint('/open', auth_required=False)
@@ -232,7 +234,7 @@ class TestAuth(BaseTest):
 
             # Check using curl
             curl = shutil.which('curl')
-            if curl:
+            if curl and not (is_ci and ismacos):  # curl mysteriously returns b'' in CI with no errors
                 def docurl(data, *args):
                     cmd = [curl, '--silent'] + list(args) + ['http://localhost:%d/closed' % server.address[1]]
                     p = subprocess.Popen(cmd, stdin=subprocess.DEVNULL, stdout=subprocess.PIPE, stderr=subprocess.PIPE)