diff --git a/Modules/_hashopenssl.c b/Modules/_hashopenssl.c
index 1a11bb5b513..b4c5b511ee6 100644
--- a/Modules/_hashopenssl.c
+++ b/Modules/_hashopenssl.c
@@ -670,7 +670,7 @@ pbkdf2_hmac(PyObject *self, PyObject *args, PyObject *kwdict)
     key = PyBytes_AS_STRING(key_obj);
 
     Py_BEGIN_ALLOW_THREADS
-    retval = PKCS5_PBKDF2_HMAC_fast((char*)password.buf, password.len,
+    retval = PKCS5_PBKDF2_HMAC_fast((char*)password.buf, (int)password.len,
                                     (unsigned char *)salt.buf, salt.len,
                                     iterations, digest, dklen,
                                     (unsigned char *)key);