diff --git a/test/parallel/test-fs-open-flags.js b/test/parallel/test-fs-open-flags.js
index 878726580b..ee33806911 100644
--- a/test/parallel/test-fs-open-flags.js
+++ b/test/parallel/test-fs-open-flags.js
@@ -10,6 +10,7 @@ const O_CREAT = fs.constants.O_CREAT || 0;
 const O_EXCL = fs.constants.O_EXCL || 0;
 const O_RDONLY = fs.constants.O_RDONLY || 0;
 const O_RDWR = fs.constants.O_RDWR || 0;
+const O_SYNC = fs.constants.O_SYNC || 0;
 const O_TRUNC = fs.constants.O_TRUNC || 0;
 const O_WRONLY = fs.constants.O_WRONLY || 0;
 
@@ -17,6 +18,8 @@ const { stringToFlags } = require('internal/fs');
 
 assert.strictEqual(stringToFlags('r'), O_RDONLY);
 assert.strictEqual(stringToFlags('r+'), O_RDWR);
+assert.strictEqual(stringToFlags('rs+'), O_RDWR | O_SYNC);
+assert.strictEqual(stringToFlags('sr+'), O_RDWR | O_SYNC);
 assert.strictEqual(stringToFlags('w'), O_TRUNC | O_CREAT | O_WRONLY);
 assert.strictEqual(stringToFlags('w+'), O_TRUNC | O_CREAT | O_RDWR);
 assert.strictEqual(stringToFlags('a'), O_APPEND | O_CREAT | O_WRONLY);