diff --git a/system/src/Grav/Common/Data/Validation.php b/system/src/Grav/Common/Data/Validation.php
index 9f0266bd4..9387effba 100644
--- a/system/src/Grav/Common/Data/Validation.php
+++ b/system/src/Grav/Common/Data/Validation.php
@@ -283,7 +283,7 @@ class Validation
 
     protected static function filterFile($value, array $params, array $field)
     {
-        if ($field['multiple'] == true) {
+        if (isset($field['multiple']) && $field['multiple'] == true) {
             return (array) $value;
         }