diff --git a/src/EioDriver.php b/src/EioDriver.php
index d1435f9..458c2f9 100644
--- a/src/EioDriver.php
+++ b/src/EioDriver.php
@@ -29,7 +29,11 @@ public function __construct()
      */
     public function open(string $path, string $mode): Promise
     {
-        $flags = \EIO_O_NONBLOCK | \EIO_O_FSYNC | $this->parseMode($mode);
+        $flags = \EIO_O_NONBLOCK | $this->parseMode($mode);
+        if (\defined('\EIO_O_FSYNC')) {
+            $flags |= \EIO_O_FSYNC;
+        }
+
         $chmod = ($flags & \EIO_O_CREAT) ? 0644 : 0;
 
         $deferred = new Deferred;