diff --git a/src/dio.c b/src/dio.c
index 0cac05f..51c1308 100644
--- a/src/dio.c
+++ b/src/dio.c
@@ -92,7 +92,7 @@ PHP_FUNCTION(dio_open)
 	zend_long      mode = 0;
 	int       fd;
 
-	if (zend_parse_parameters(ZEND_NUM_ARGS(), "sl|l", &file_name, &file_name_length, &flags, &mode) == FAILURE) {
+	if (zend_parse_parameters(ZEND_NUM_ARGS(), "pl|l", &file_name, &file_name_length, &flags, &mode) == FAILURE) {
 		RETURN_THROWS();
 	}
 
diff --git a/src/dio_stream_wrappers.c b/src/dio_stream_wrappers.c
index e55c580..ca44d2d 100644
--- a/src/dio_stream_wrappers.c
+++ b/src/dio_stream_wrappers.c
@@ -198,7 +198,7 @@ PHP_FUNCTION(dio_raw) {
 	char *mode;
 	size_t mode_len;
 
-	if (zend_parse_parameters(ZEND_NUM_ARGS(), "ss|h!", &filename, &filename_len, &mode, &mode_len, &options) == FAILURE) {
+	if (zend_parse_parameters(ZEND_NUM_ARGS(), "ps|h!", &filename, &filename_len, &mode, &mode_len, &options) == FAILURE) {
 		RETURN_THROWS();
 	}
 
@@ -353,7 +353,7 @@ PHP_FUNCTION(dio_serial) {
 	char *mode;
 	size_t mode_len;
 
-	if (zend_parse_parameters(ZEND_NUM_ARGS(), "ss|h!", &filename, &filename_len, &mode, &mode_len, &options) == FAILURE) {
+	if (zend_parse_parameters(ZEND_NUM_ARGS(), "ps|h!", &filename, &filename_len, &mode, &mode_len, &options) == FAILURE) {
 		RETURN_THROWS();
 	}