diff --git a/src/Config.php b/src/Config.php
index 4efcbb7..690e64d 100644
--- a/src/Config.php
+++ b/src/Config.php
@@ -4,6 +4,7 @@
 
 use ArrayAccess;
 use Iterator;
+use RuntimeException;
 
 /**
  * Simple class for managing a configuration array