diff --git a/setup.py b/setup.py
index f1341cc0c..7b81a68c2 100755
--- a/setup.py
+++ b/setup.py
@@ -236,8 +236,8 @@ def log( text):
 g_pymupdfb_sdist_marker = 'pymupdfb_sdist'
 
 PYMUPDF_SETUP_PY_LIMITED_API = os.environ.get('PYMUPDF_SETUP_PY_LIMITED_API')
-assert PYMUPDF_SETUP_PY_LIMITED_API in (None, '0', '1'), \
-        f'Should be "0", "1" or undefined: {PYMUPDF_SETUP_PY_LIMITED_API=}.'
+assert PYMUPDF_SETUP_PY_LIMITED_API in (None, '', '0', '1'), \
+        f'Should be "", "0", "1" or undefined: {PYMUPDF_SETUP_PY_LIMITED_API=}.'
 g_py_limited_api = (PYMUPDF_SETUP_PY_LIMITED_API != '0')
 
 PYMUPDF_SETUP_URL_WHEEL =  os.environ.get('PYMUPDF_SETUP_URL_WHEEL')