diff --git a/ext/gmp/gmp.c b/ext/gmp/gmp.c
index 1d87695c6e335..a23263d407e6f 100644
--- a/ext/gmp/gmp.c
+++ b/ext/gmp/gmp.c
@@ -96,7 +96,7 @@ PHP_GMP_API zend_class_entry *php_gmp_class_entry(void) {
 	((__GNU_MP_VERSION >= 6) || (__GNU_MP_VERSION >= 5 && __GNU_MP_VERSION_MINOR >= 1))
 
 #define IS_GMP(zval) \
-	(Z_TYPE_P(zval) == IS_OBJECT && instanceof_function(Z_OBJCE_P(zval), gmp_ce))
+	(Z_TYPE_P(zval) == IS_OBJECT && Z_OBJCE_P(zval) == gmp_ce)
 
 #define GET_GMP_OBJECT_FROM_OBJ(obj) \
 	php_gmp_object_from_zend_object(obj)
@@ -116,7 +116,7 @@ static bool gmp_zend_parse_arg_into_mpz_ex(
 	bool is_operator
 ) {
 	if (EXPECTED(Z_TYPE_P(arg) == IS_OBJECT)) {
-		if (EXPECTED(instanceof_function(Z_OBJCE_P(arg), gmp_ce))) {
+		if (EXPECTED(Z_OBJCE_P(arg) == gmp_ce)) {
 			*destination_mpz_ptr = GET_GMP_FROM_ZVAL(arg);
 			return true;
 		}
@@ -404,7 +404,7 @@ typeof_op_failure: ;
 
 static zend_result gmp_do_operation_ex(uint8_t opcode, zval *result, zval *op1, zval *op2) /* {{{ */
 {
-	mpz_ptr gmp_op1, gmp_result;
+	mpz_ptr gmp_result;
 	switch (opcode) {
 	case ZEND_ADD:
 		return binop_operator_helper(mpz_add, result, op1, op2);
@@ -429,11 +429,9 @@ static zend_result gmp_do_operation_ex(uint8_t opcode, zval *result, zval *op1,
 	case ZEND_BW_XOR:
 		return binop_operator_helper(mpz_xor, result, op1, op2);
 	case ZEND_BW_NOT: {
-		if (!gmp_zend_parse_arg_into_mpz_ex(op1, &gmp_op1, 1, false)) {
-			return FAILURE;
-		}
+		ZEND_ASSERT(Z_TYPE_P(op1) == IS_OBJECT && Z_OBJCE_P(op1) == gmp_ce);
 		gmp_create(result, &gmp_result);
-		mpz_com(gmp_result, gmp_op1);
+		mpz_com(gmp_result, GET_GMP_FROM_ZVAL(op1));
 		return SUCCESS;
 	}