From 4c9cf7439f8e769af600c87190a44367583526cb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Javier=20S=C3=A1nchez=20Castro?=
 <72013291+JavierSanchezCastro@users.noreply.github.com>
Date: Thu, 30 Oct 2025 13:06:06 +0100
Subject: [PATCH] Update fastapi/routing.py

Co-authored-by: Motov Yurii <109919500+YuriiMotov@users.noreply.github.com>
---
 fastapi/routing.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fastapi/routing.py b/fastapi/routing.py
index eb3d2c620..a6ed2f328 100644
--- a/fastapi/routing.py
+++ b/fastapi/routing.py
@@ -1333,7 +1333,10 @@ class APIRouter(routing.Router):
         app.include_router(internal_router)
         ```
         """
-        assert self is not router, "Cannot include router into itself"
+        assert self is not router, (
+            "Cannot include the same APIRouter instance into itself. "
+            "Did you mean to include a different router?"
+        )
         if prefix:
             assert prefix.startswith("/"), "A path prefix must start with '/'"
             assert not prefix.endswith("/"), (