diff --git a/src/Forms/FieldList.php b/src/Forms/FieldList.php
index 7e8a80cd1..85143cf13 100644
--- a/src/Forms/FieldList.php
+++ b/src/Forms/FieldList.php
@@ -3,6 +3,7 @@
 namespace SilverStripe\Forms;
 
 use SilverStripe\ORM\ArrayList;
+use SilverStripe\Dev\Deprecation;
 
 /**
  * A list designed to hold form field instances.
@@ -218,6 +219,10 @@ class FieldList extends ArrayList
      */
     public function addFieldsToTab($tabName, $fields, $insertBefore = null)
     {
+        if (!is_array($fields)) {
+            Deprecation::notice('5.3.0', '$fields will need to be passed as an array in CMS 6', Deprecation::SCOPE_METHOD);
+        }
+
         $this->flushFieldsCache();
 
         // Find the tab
@@ -270,6 +275,10 @@ class FieldList extends ArrayList
      */
     public function removeFieldsFromTab($tabName, $fields)
     {
+        if (!is_array($fields)) {
+            Deprecation::notice('5.3.0', '$fields will need to be passed as an array in CMS 6', Deprecation::SCOPE_METHOD);
+        }
+
         $this->flushFieldsCache();
 
         // Find the tab