diff --git a/docs/en/docs/release-notes.md b/docs/en/docs/release-notes.md
index 71dc7bb74..495bf83b4 100644
--- a/docs/en/docs/release-notes.md
+++ b/docs/en/docs/release-notes.md
@@ -7,6 +7,11 @@ hide:
 
 ## Latest Changes
 
+### Features
+
+* ✨ Show a clear error on attempt to include router into itself. PR [#14258](https://github.com/fastapi/fastapi/pull/14258) by [@JavierSanchezCastro](https://github.com/JavierSanchezCastro).
+* ✨ Replace `dict` by `Mapping` on `HTTPException.headers`. PR [#12997](https://github.com/fastapi/fastapi/pull/12997) by [@rijenkii](https://github.com/rijenkii).
+
 ### Internal
 
 * 🔧 Configure `test` workflow to run tests with `inline-snapshot=review`. PR [#14876](https://github.com/fastapi/fastapi/pull/14876) by [@YuriiMotov](https://github.com/YuriiMotov).
diff --git a/fastapi/exceptions.py b/fastapi/exceptions.py
index 62b4674de..9924d0e2b 100644
--- a/fastapi/exceptions.py
+++ b/fastapi/exceptions.py
@@ -1,4 +1,4 @@
-from collections.abc import Sequence
+from collections.abc import Mapping, Sequence
 from typing import Annotated, Any, Optional, TypedDict, Union
 
 from annotated_doc import Doc
@@ -68,7 +68,7 @@ class HTTPException(StarletteHTTPException):
             ),
         ] = None,
         headers: Annotated[
-            Optional[dict[str, str]],
+            Optional[Mapping[str, str]],
             Doc(
                 """
                 Any headers to send to the client in the response.
diff --git a/fastapi/routing.py b/fastapi/routing.py
index 16a89ef3e..ed873fda8 100644
--- a/fastapi/routing.py
+++ b/fastapi/routing.py
@@ -1393,6 +1393,10 @@ 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)