diff --git a/src/Teller.php b/src/Teller.php
index 846f009..9354d65 100644
--- a/src/Teller.php
+++ b/src/Teller.php
@@ -121,7 +121,7 @@ class Teller implements SimpleCache\CacheInterface, LoggerAwareInterface {
 	 *   MUST be thrown if $keys is neither an array nor a Traversable,
 	 *   or if any of the $keys are not a legal value.
 	 */
-	public function getMultiple($keys, $default = null)
+	public function getMultiple(iterable $keys, mixed $default = null): iterable
 	{
 		// Check type of keys
 		if ( ! is_iterable($keys))