diff --git a/src/python/ttfautohint/__init__.py b/src/python/ttfautohint/__init__.py
index c201c39..ec26c91 100644
--- a/src/python/ttfautohint/__init__.py
+++ b/src/python/ttfautohint/__init__.py
@@ -58,6 +58,10 @@ def __init__(self, path=None, **kwargs):
         version_string = lib.TTF_autohint_version_string().decode('ascii')
         self.version_string = version_string
 
+        # In the M1 ABI, ctypes counts the number of fixed arguments
+        # when building the varargs array. See https://bugs.python.org/issue42880
+        lib.TTF_autohint.argtypes = [c_char_p]
+
     def _build_info_data(self, options):
         # as a side effect, these arguments are popped from the options dict
         # as they are not part of TTF_autohint API