diff --git a/fastapi/routing.py b/fastapi/routing.py
index 9be2b44bc..32d0e3090 100644
--- a/fastapi/routing.py
+++ b/fastapi/routing.py
@@ -1388,6 +1388,10 @@ class APIRouter(routing.Router):
         app.include_router(internal_router)
         ```
         """
+        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("/"), (
diff --git a/tests/test_router_circular_import.py b/tests/test_router_circular_import.py
new file mode 100644
index 000000000..492a26d00
--- /dev/null
+++ b/tests/test_router_circular_import.py
@@ -0,0 +1,12 @@
+import pytest
+from fastapi import APIRouter
+
+
+def test_router_circular_import():
+    router = APIRouter()
+
+    with pytest.raises(
+        AssertionError,
+        match="Cannot include the same APIRouter instance into itself. Did you mean to include a different router?",
+    ):
+        router.include_router(router)