diff --git a/README.md b/README.md
index d9495b5..03e3621 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,11 @@ Installation:
   modules directory from your website (typically sites/all/modules).
 
 Dependencies:
-  The basic CAPTCHA module has no dependencies, nothing special is required.
+  The basic CAPTCHA module requires
+  PHP Captcha library Gregwar/Captcha (https://github.com/Gregwar/Captcha).
+  To install it add contains of captcha/composer.json to
+  your composer.json file or run:
+    composer require gregwar/captcha:1.0.11
 
 Conflicts/known issues:
   CAPTCHA and page caching do not work together currently.
diff --git a/captcha.inc b/captcha.inc
index b0e5abf..5505714 100644
--- a/captcha.inc
+++ b/captcha.inc
@@ -217,7 +217,7 @@ function _captcha_get_captcha_placement($form_id, $form) {
       }
       else {
         // Use NULL when no buttons were found.
-        $placement = NULL;
+        $placement = array();
       }
     }
 
diff --git a/composer.json b/composer.json
new file mode 100644
index 0000000..278f942
--- /dev/null
+++ b/composer.json
@@ -0,0 +1,5 @@
+{
+  "require": {
+    "gregwar/captcha": "1.0.11"
+  }
+}