--- setup.py
+++ setup.py	2024-09-24 19:25:00.000000000 +0800
@@ -121,6 +121,8 @@
         compile_args = ['-fPIC']
     else:
         compile_args = shlex.split(get_output(f"{kc} --cflags gssapi"))
+        if sys.platform == 'darwin':
+            compile_args.append('-std=c99')
 
 # add in the extra workarounds for different include structures
 if winkrb_path:
