From 111de8995783ca3a8b8bbdbabae6d15bb2009ffa Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Javier=20S=C3=A1nchez?= <javier.sanchez.castro@bookline.ai>
Date: Thu, 30 Oct 2025 10:50:23 +0100
Subject: [PATCH] Add check for ciruclar imports + test

---
 fastapi/routing.py                   |  1 +
 tests/test_router_circular_import.py | 11 +++++++++++
 2 files changed, 12 insertions(+)
 create mode 100644 tests/test_router_circular_import.py

diff --git a/fastapi/routing.py b/fastapi/routing.py
index 0b59d250a..eb3d2c620 100644
--- a/fastapi/routing.py
+++ b/fastapi/routing.py
@@ -1333,6 +1333,7 @@ class APIRouter(routing.Router):
         app.include_router(internal_router)
         ```
         """
+        assert self is not router, "Cannot include router into itself"
         if prefix:
             assert prefix.startswith("/"), "A path prefix must start with '/'"
             assert not prefix.endswith("/"), (
diff --git a/tests/test_router_circular_import.py b/tests/test_router_circular_import.py
new file mode 100644
index 000000000..dfec8d24c
--- /dev/null
+++ b/tests/test_router_circular_import.py
@@ -0,0 +1,11 @@
+import pytest
+from fastapi import APIRouter, FastAPI
+
+
+def test_router_circular_import():
+    app = FastAPI()
+    router = APIRouter()
+
+    app.include_router(router)
+    with pytest.raises(AssertionError, match="Router cannot be the same as parent"):
+        router.include_router(router)
\ No newline at end of file