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("/"), (