diff --git a/GoogleStrategy.php b/GoogleStrategy.php
index 30c7cdd..5f4556c 100644
--- a/GoogleStrategy.php
+++ b/GoogleStrategy.php
@@ -27,7 +27,7 @@ class GoogleStrategy extends OpauthStrategy{
 	/**
 	 * Optional config keys, without predefining any default values.
 	 */
-	public $optionals = array('redirect_uri', 'scope', 'state', 'access_type', 'approval_prompt');
+	public $optionals = array('redirect_uri', 'scope', 'state', 'access_type', 'approval_prompt','prompt');
 	
 	/**
 	 * Optional config keys with respective default values, listed as associative arrays
@@ -148,4 +148,4 @@ private function userinfo($access_token){
 			$this->errorCallback($error);
 		}
 	}
-}
\ No newline at end of file
+}