diff --git a/schema/datatypes/anat.json b/schema/datatypes/anat.json
index ebcf58a8..27fb9c8a 100644
--- a/schema/datatypes/anat.json
+++ b/schema/datatypes/anat.json
@@ -159,7 +159,7 @@
       "ceagent": "optional",
       "reconstruction": "optional",
       "echo": "optional",
-      "flip": "required",
+      "flip": "optional",
       "inversion": "required",
       "part": "optional"
     }