diff --git a/php/tests/php_implementation_test.php b/php/tests/php_implementation_test.php
index 8d27d19..307b749 100644
--- a/php/tests/php_implementation_test.php
+++ b/php/tests/php_implementation_test.php
@@ -14,8 +14,19 @@
 use Google\Protobuf\Internal\GPBWire;
 use Google\Protobuf\Internal\CodedOutputStream;
 
+/**
+ * Please note, this test is only intended to be run without the protobuf C
+ * extension.
+ */
 class ImplementationTest extends TestBase
 {
+    public function setUp()
+    {
+        if (extension_loaded('protobuf')) {
+            $this->markTestSkipped();
+        }
+    }
+
     public function testReadInt32()
     {
         $value = null;