diff --git a/api/s33_region.py b/api/s33_region.py
index 7ef0f1e..9d90e20 100644
--- a/api/s33_region.py
+++ b/api/s33_region.py
@@ -32,7 +32,8 @@ def _set_region(name: str, cs: ChangeSet) -> DbChangeSet:
 def set_region(name: str, cs: ChangeSet) -> ChangeSet:
     if 'id' not in cs.operations[0] or 'boundary' not in cs.operations[0]:
         return ChangeSet()
-    if len(cs.operations[0]['boundary']) < 3:
+    b = cs.operations[0]['boundary']
+    if len(b) < 4 or b[0] != b[-1]:
         return ChangeSet()
     if get_region(name, cs.operations[0]['id']) == {}:
         return ChangeSet()
@@ -54,7 +55,8 @@ def _add_region(name: str, cs: ChangeSet) -> DbChangeSet:
 def add_region(name: str, cs: ChangeSet) -> ChangeSet:
     if 'id' not in cs.operations[0] or 'boundary' not in cs.operations[0]:
         return ChangeSet()
-    if len(cs.operations[0]['boundary']) < 3:
+    b = cs.operations[0]['boundary']
+    if len(b) < 4 or b[0] != b[-1]:
         return ChangeSet()
     if get_region(name, cs.operations[0]['id']) != {}:
         return ChangeSet()