diff --git a/library/Director/CustomVariable/CustomVariableString.php b/library/Director/CustomVariable/CustomVariableString.php
index ab14e77a..fdd73804 100644
--- a/library/Director/CustomVariable/CustomVariableString.php
+++ b/library/Director/CustomVariable/CustomVariableString.php
@@ -8,6 +8,10 @@ class CustomVariableString extends CustomVariable
 {
     public function equals(CustomVariable $var)
     {
+        if (! $var instanceof CustomVariableString) {
+            return false;
+        }
+
         return $var->getValue() === $this->getValue();
     }