--- a/ext/session/session.c
+++ b/ext/session/session.c
@@ -3161,6 +3161,9 @@
 				} else {
 					if (!Z_ISUNDEF(progress->data)) {
 						SEPARATE_ARRAY(&progress->data);
+						progress->post_bytes_processed = zend_hash_str_find(
+							Z_ARRVAL(progress->data), "bytes_processed",
+							sizeof("bytes_processed") - 1);
 						add_assoc_bool_ex(&progress->data, "done", sizeof("done") - 1, 1);
 						Z_LVAL_P(progress->post_bytes_processed) = data->post_bytes_processed;
 						php_session_rfc1867_update(progress, 1);