diff --git a/x-pack/plugins/upgrade_assistant/server/lib/reindexing/index_settings.test.ts b/x-pack/plugins/upgrade_assistant/server/lib/reindexing/index_settings.test.ts
index 957198cde8da9..0c31a5b8d2fe5 100644
--- a/x-pack/plugins/upgrade_assistant/server/lib/reindexing/index_settings.test.ts
+++ b/x-pack/plugins/upgrade_assistant/server/lib/reindexing/index_settings.test.ts
@@ -64,6 +64,7 @@ describe('transformFlatSettings', () => {
           'index.verified_before_close': 'true',
           'index.version.created': '123123',
           'index.version.upgraded': '123123',
+          'index.mapper.dynamic': 'true',
 
           // Deprecated settings
           'index.force_memory_term_dictionary': '1024',
diff --git a/x-pack/plugins/upgrade_assistant/server/lib/reindexing/index_settings.ts b/x-pack/plugins/upgrade_assistant/server/lib/reindexing/index_settings.ts
index b65984af5deb3..870dd3ae45c30 100644
--- a/x-pack/plugins/upgrade_assistant/server/lib/reindexing/index_settings.ts
+++ b/x-pack/plugins/upgrade_assistant/server/lib/reindexing/index_settings.ts
@@ -178,6 +178,9 @@ const removeUnsettableSettings = (settings: FlatSettings['settings']) =>
     'index.verified_before_close',
     'index.version.created',
 
+    // Ignored since 6.x and forbidden in 7.x
+    'index.mapper.dynamic',
+
     // Deprecated in 9.0
     'index.version.upgraded',
   ]);