diff --git a/libs/cli/langgraph_cli/deploy.py b/libs/cli/langgraph_cli/deploy.py
index dd4e7e051..525f9d5de 100644
--- a/libs/cli/langgraph_cli/deploy.py
+++ b/libs/cli/langgraph_cli/deploy.py
@@ -512,6 +512,12 @@ def find_deployment_by_name(
     for resource in listed:
         if resource.get("name") == name and resource.get("id"):
             return ExistingDeployment(str(resource["id"]), _source_of(resource))
+    if len(listed) >= MAX_PAGE_SIZE:
+        raise click.ClickException(
+            "This workspace has more deployments than the CLI can search, so it "
+            f"cannot tell whether '{name}' already exists. Pass --deployment-id to "
+            "update an existing deployment."
+        )
     return None
 
 
diff --git a/libs/cli/tests/unit_tests/test_deploy_helpers.py b/libs/cli/tests/unit_tests/test_deploy_helpers.py
index 292aff97e..3ea3931a9 100644
--- a/libs/cli/tests/unit_tests/test_deploy_helpers.py
+++ b/libs/cli/tests/unit_tests/test_deploy_helpers.py
@@ -1149,3 +1149,33 @@ def test_finding_a_deployment_by_name_returns_none_when_the_server_has_no_match(
     )
 
     assert find_deployment_by_name(client, "agent") is None
+
+
+def test_a_full_page_without_a_match_refuses_to_claim_the_name_is_free():
+    page = [
+        {"id": f"dep-{index}", "name": f"other-agent-{index}"} for index in range(100)
+    ]
+    client = HostBackendClient(
+        "https://api.example.com",
+        "key",
+        transport=httpx.MockTransport(
+            lambda req: httpx.Response(200, json={"resources": page})
+        ),
+    )
+
+    with pytest.raises(click.ClickException, match="--deployment-id"):
+        find_deployment_by_name(client, "brand-new-agent")
+
+
+def test_a_partial_page_without_a_match_means_the_name_is_free():
+    client = HostBackendClient(
+        "https://api.example.com",
+        "key",
+        transport=httpx.MockTransport(
+            lambda req: httpx.Response(
+                200, json={"resources": [{"id": "dep-1", "name": "other"}]}
+            )
+        ),
+    )
+
+    assert find_deployment_by_name(client, "brand-new-agent") is None