diff --git a/injection/main.py b/injection/main.py
index 028c8e2..08b9b6e 100644
--- a/injection/main.py
+++ b/injection/main.py
@@ -2,8 +2,8 @@
 
 from contextlib import suppress
 from dataclasses import dataclass
-from threading import RLock, get_ident
-from typing import TYPE_CHECKING, Any, Generic, Literal, TypeVar, overload
+from threading import Lock, RLock, get_ident
+from typing import TYPE_CHECKING, Any, ClassVar, Generic, Literal, TypeVar, overload
 
 from injection.compat import get_frame
 
@@ -21,6 +21,8 @@
     "Injection",
     "ObjectState",
     "inject",
+    "lenient_recursion_guard",
+    "strict_recursion_guard",
 )
 
 
@@ -62,7 +64,11 @@ def __hash__(self) -> int:
         return self.hash
 
 
-def default_recursion_guard(early: EarlyObject[object]) -> Never:
+def lenient_recursion_guard(early: EarlyObject[object]) -> Never:
+    pass
+
+
+def strict_recursion_guard(early: EarlyObject[object]) -> Never:
     msg = f"{early} requested itself"
     raise RecursionError(msg)
 
@@ -73,9 +79,11 @@ class Injection(Generic[Object_co]):
     pass_scope: bool = False
     cache: bool = False
     cache_per_alias: bool = False
-    recursion_guard: Callable[[EarlyObject[Any]], object] = default_recursion_guard
+    recursion_guard: Callable[[EarlyObject[Any]], object] = lenient_recursion_guard
     debug_info: str | None = None
 
+    _reassignment_lock: ClassVar[Lock] = Lock()
+
     def _call_factory(self, scope: Locals) -> Object_co:
         if self.pass_scope:
             return self.factory(scope)
@@ -118,7 +126,10 @@ def assign_to(self, *aliases: str, scope: Locals) -> None:
                 debug_info=debug_info,
             )
             key = InjectionKey(alias, early)
-            scope[key] = early
+
+            with self._reassignment_lock:
+                scope.pop(key, None)
+                scope[key] = early
 
 
 SENTINEL = object()
@@ -247,7 +258,7 @@ def inject(  # noqa: PLR0913
     pass_scope: bool = False,
     cache: bool = False,
     cache_per_alias: bool = False,
-    recursion_guard: Callable[[EarlyObject[Any]], object] = default_recursion_guard,
+    recursion_guard: Callable[[EarlyObject[Any]], object] = strict_recursion_guard,
     debug_info: str | None = None,
 ) -> None:
     """
diff --git a/tests/unit_tests/test_main.py b/tests/unit_tests/test_main.py
index e164e3b..e63d017 100644
--- a/tests/unit_tests/test_main.py
+++ b/tests/unit_tests/test_main.py
@@ -5,7 +5,7 @@
 
 import pytest
 
-from injection import Injection, inject
+from injection import Injection, inject, lenient_recursion_guard
 
 
 def test_injection_basic() -> None:
@@ -211,11 +211,18 @@ def test_injection_recursive_guard() -> None:
     def factory() -> str:
         return scope.get("my_alias", "default_value")
 
-    inject("my_alias", into=scope, factory=factory)
+    inject(
+        "my_alias", into=scope, factory=factory, recursion_guard=lenient_recursion_guard
+    )
 
     obj = scope["my_alias"]
     assert obj == "default_value"
 
+    inject("my_alias", into=scope, factory=factory)  # strict
+
+    with pytest.raises(RecursionError, match="requested itself"):
+        obj = scope["my_alias"]
+
 
 def test_injection_with_no_aliases() -> None:
     """Test that injection with no aliases raises an error."""