diff --git a/src/Shm/SharedMemoryBlock.php b/src/Shm/SharedMemoryBlock.php
index ec23762..63803b6 100644
--- a/src/Shm/SharedMemoryBlock.php
+++ b/src/Shm/SharedMemoryBlock.php
@@ -29,7 +29,7 @@ class SharedMemoryBlock
      */
     public function __construct(KeyInterface $key, string $flags, int $memsize, int $perm = 0666)
     {
-        if (!($shm_resource = shmop_open($key->getKey(), $memsize, $perm))) {
+        if (!($shm_resource = shmop_open($key->getKey(), $flags, $perm, $memsize))) {
             throw new \RuntimeException("Unable to attach shm resource {$key}");
         }
         
diff --git a/tests/Shm/SharedMemoryBlockTest.php b/tests/Shm/SharedMemoryBlockTest.php
new file mode 100644
index 0000000..a1b794a
--- /dev/null
+++ b/tests/Shm/SharedMemoryBlockTest.php
@@ -0,0 +1,25 @@
+<?php
+
+namespace NoccyLabs\Ipc\Shm;
+
+use NoccyLabs\Ipc\Key\FileKey;
+
+
+
+
+
+class SharedMemoryBlockTest extends \PhpUnit\Framework\TestCase
+{
+    public function testWritingAndReading()
+    {
+        $key = new FileKey(__DIR__);
+        $shm = new SharedMemoryBlock($key, SharedMemoryBlock::FLAG_CREATE, 64);
+
+        $this->assertEquals(11, $shm->write("Hello World", 0));
+        $this->assertEquals("Hello World", $shm->read(11, 0));
+        $this->assertEquals(3, $shm->write("foo", 2));
+        $this->assertEquals("Hefoo World", $shm->read(11, 0));
+    
+        $shm->destroy();
+    }
+}
\ No newline at end of file