diff --git a/src/session_ops/zendesk/api.py b/src/session_ops/zendesk/api.py
index 37290fa..9c0b83a 100644
--- a/src/session_ops/zendesk/api.py
+++ b/src/session_ops/zendesk/api.py
@@ -236,7 +236,11 @@ def has_open_chat(session, subdomain, ticket_id):
 
 def unassign(session, subdomain, ticket_id):
     """Clear the ticket's assignee, which is what lets Zendesk end its live chat.
-    Returns whether Zendesk took it."""
+    Returns whether the ticket Zendesk sent back has no assignee.
+
+    A 200 is not enough: on a ticket with a live chat open, Zendesk can answer 200 and
+    keep the assignee.
+    """
     url = f"https://{subdomain}.zendesk.com/api/v2/tickets/{ticket_id}.json"
     try:
         resp = session.request("PUT", url, json={"ticket": {"assignee_id": None}})
@@ -246,6 +250,13 @@ def unassign(session, subdomain, ticket_id):
     if resp.status_code >= 400:
         print(f"Note: unassigning #{ticket_id} returned {resp.status_code}.")
         return False
+    try:
+        ticket = resp.json().get("ticket") or {}
+    except ValueError:
+        ticket = {}
+    if "assignee_id" not in ticket or ticket["assignee_id"] is not None:
+        print(f"Note: Zendesk accepted unassigning #{ticket_id} but kept its assignee.")
+        return False
     return True
 
 
diff --git a/tests/zendesk/test_triage.py b/tests/zendesk/test_triage.py
index c896992..52d21dc 100644
--- a/tests/zendesk/test_triage.py
+++ b/tests/zendesk/test_triage.py
@@ -809,9 +809,13 @@ def test_released_tickets_are_listed_apart_from_stuck_ones(self):
         self.assertIn("[#2]", lines[1])
 
     def test_release_unassigns_each_and_keeps_what_zendesk_took(self):
-        session = FakeSession([FakeResponse({}), FakeResponse({}, status_code=403)])
+        session = FakeSession([
+            FakeResponse({"ticket": {"id": 4, "assignee_id": None}}),
+            FakeResponse({}, status_code=403),
+            FakeResponse({"ticket": {"id": 6, "assignee_id": 77}}),
+            FakeResponse({})])
         with contextlib.redirect_stdout(io.StringIO()):
-            released = triage.release_open_chats(session, "acme", [4, 5])
+            released = triage.release_open_chats(session, "acme", [4, 5, 6, 7])
         self.assertEqual(released, {4})
         method, url, kwargs = session.calls[0]
         self.assertEqual(method, "PUT")