diff --git a/tools/ci/issue_claim.py b/tools/ci/issue_claim.py
index 4da1a381ae9..d077c13a480 100644
--- a/tools/ci/issue_claim.py
+++ b/tools/ci/issue_claim.py
@@ -228,12 +228,14 @@ def get_permission(self, repository, actor):
                 return {}
             raise
 
-    def can_assign(self, repository, actor):
+    def can_assign(self, repository, issue_number, actor):
         try:
             self.request(
                 "GET",
-                "{}/assignees/{}".format(
-                    self._repository_path(repository), quote(actor, safe="")
+                "{}/issues/{}/assignees/{}".format(
+                    self._repository_path(repository),
+                    issue_number,
+                    quote(actor, safe=""),
                 ),
                 expected=(204,),
             )
@@ -462,7 +464,9 @@ def handle_claim(client, context, comments):
         post_result(client, context, rejection_message("claim", latest))
         return "race_{}".format(latest.reason)
 
-    assignable = client.can_assign(context.repository, context.actor)
+    assignable = client.can_assign(
+        context.repository, context.issue_number, context.actor
+    )
     if assignable:
         client.add_assignees(context.repository, context.issue_number, (context.actor,))
     confirmed_issue = client.get_issue(context.repository, context.issue_number)
diff --git a/tools/ci/test_issue_claim.py b/tools/ci/test_issue_claim.py
index 9aa265bbdcb..cdda0ac8a8d 100644
--- a/tools/ci/test_issue_claim.py
+++ b/tools/ci/test_issue_claim.py
@@ -75,8 +75,8 @@ def get_permission(self, repository, actor):
         self.calls.append(("get_permission", repository, actor))
         return self.permission
 
-    def can_assign(self, repository, actor):
-        self.calls.append(("can_assign", repository, actor))
+    def can_assign(self, repository, issue_number, actor):
+        self.calls.append(("can_assign", repository, issue_number, actor))
         return self.assignable
 
     def get_label(self, repository, label):
@@ -91,6 +91,28 @@ def remove_label(self, repository, issue_number, label):
 
 
 class ClientTests(unittest.TestCase):
+    def test_assignability_is_checked_for_specific_issue(self):
+        class RecordingClient(issue_claim.GitHubClient):
+            def __init__(self):
+                self.call = None
+
+            def request(self, *args, **kwargs):
+                self.call = (args, kwargs)
+
+        client = RecordingClient()
+
+        self.assertTrue(
+            client.can_assign("RT-Thread/rt-thread", 42, "external-user")
+        )
+        self.assertEqual(
+            client.call[0],
+            (
+                "GET",
+                "/repos/RT-Thread/rt-thread/issues/42/assignees/external-user",
+            ),
+        )
+        self.assertEqual(client.call[1]["expected"], (204,))
+
     def test_comment_creation_disables_automatic_retries(self):
         class RecordingClient(issue_claim.GitHubClient):
             def __init__(self):
@@ -254,6 +276,9 @@ def test_successful_claim_rechecks_and_confirms_state(self):
         result = issue_claim.handle_event(make_event(), client)
 
         self.assertEqual(result, "claimed")
+        self.assertIn(
+            ("can_assign", "RT-Thread/rt-thread", 42, "alice"), client.calls
+        )
         self.assertIn(
             ("add_assignees", "RT-Thread/rt-thread", 42, ("alice",)),
             client.calls,