diff --git a/src/BaseInputFilter.php b/src/BaseInputFilter.php
index 7a0edf0c..d6364623 100644
--- a/src/BaseInputFilter.php
+++ b/src/BaseInputFilter.php
@@ -497,7 +497,7 @@ public function getMessages()
     protected function validateValidationGroup(array $inputs)
     {
         foreach ($inputs as $name) {
-            if (! is_string($name) || ! array_key_exists($name, $this->inputs)) {
+            if (! array_key_exists($name, $this->inputs)) {
                 throw new Exception\InvalidArgumentException(sprintf(
                     'setValidationGroup() expects a list of valid input names; "%s" was not found',
                     (string) $name