diff --git a/system/libraries/Form_validation.php b/system/libraries/Form_validation.php
index 77c968e..6cbe032 100644
--- a/system/libraries/Form_validation.php
+++ b/system/libraries/Form_validation.php
@@ -187,6 +187,12 @@
 			return $this;
 		}
 
+		// Convert an array of rules to a string
+		if (is_array($rules))
+		{
+			$rules = implode('|', $rules);
+		}
+
 		// No fields? Nothing to do...
 		if ( ! is_string($field) OR ! is_string($rules) OR $field === '')
 		{