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Co-Authored-By: Gina Peter Banyard <girgias@php.net>

Author: LamentXU123

ext/gmp/gmp.c

@@ -1206,6 +1206,7 @@ ZEND_FUNCTION(gmp_powm_sec)
 		RETURN_THROWS();
 	}
 
+	/* Zero is not odd, so this also rejects a zero modulus. */
 	if (!mpz_odd_p(gmpnum_mod)) {
 		zend_argument_value_error(3, "must be odd");
 		RETURN_THROWS();