diff --git a/src/Api/Serializer/MailDriverSerializer.php b/src/Api/Serializer/MailDriverSerializer.php
index 6cdbad75c..03a23dcfe 100644
--- a/src/Api/Serializer/MailDriverSerializer.php
+++ b/src/Api/Serializer/MailDriverSerializer.php
@@ -33,10 +33,20 @@ class MailDriverSerializer extends AbstractSerializer
             );
         }
 
-        $driver = $driver['driver'];
+        $settings = $driver['driver']->availableSettings();
+
+        if (key($settings) === 0) {
+            // BACKWARDS COMPATIBILITY: Support a simple list of fields (without
+            // type or additional metadata).
+            // Turns ["f1", "f2"] into {"f1": "", "f2": ""}
+            // @deprecated since 0.1.0-beta.12
+            $settings = array_reduce($settings, function ($memo, $key) {
+                return [$key => ''] + $memo;
+            }, []);
+        }
 
         return [
-            'fields' => $driver->availableSettings(),
+            'fields' => $settings,
         ];
     }