diff --git a/Herbert/Framework/Shortcode.php b/Herbert/Framework/Shortcode.php
index 4e99072..25b65b4 100644
--- a/Herbert/Framework/Shortcode.php
+++ b/Herbert/Framework/Shortcode.php
@@ -41,7 +41,7 @@ public function add($name, $callable, $arguments = [])
                 $attributes = $this->renameArguments($arguments, $attributes);
             }
 
-            if (strpos($callable, '::') !== false)
+            if (is_string($callable) && strpos($callable, '::') !== false)
             {
                 list($api, $method) = explode('::', $callable);