diff --git a/aioinject/providers.py b/aioinject/providers.py
index 51b5ee6..5d0571d 100644
--- a/aioinject/providers.py
+++ b/aioinject/providers.py
@@ -96,7 +96,7 @@ def _typevar_map(
         if not origin:
             continue
 
-        params = origin.__parameters__
+        params = getattr(origin, "__parameters__", ())
         args = typing.get_args(base)
         typevar_map |= dict(zip(params, args, strict=False))
 
diff --git a/tests/features/test_generics.py b/tests/features/test_generics.py
index bd28159..4aaafdb 100644
--- a/tests/features/test_generics.py
+++ b/tests/features/test_generics.py
@@ -1,5 +1,7 @@
 from typing import Generic, TypeVar
 
+import pytest
+
 from aioinject import Container, Object, Scoped
 from aioinject.providers import Dependency
 
@@ -43,11 +45,23 @@ async def test_generic_dependency() -> None:
     )
 
 
-async def test_resolve_generics() -> None:
+@pytest.mark.parametrize(
+    ("type_", "instanceof"),
+    [
+        (GenericService, GenericService),
+        (WithGenericDependency[int], WithGenericDependency),
+        (ConstrainedGenericDependency, ConstrainedGenericDependency),
+    ],
+)
+async def test_resolve_generics(
+    type_: type[object],
+    instanceof: type[object],
+) -> None:
     container = Container()
-    container.register(Scoped(WithGenericDependency[int]))
+    container.register(Scoped(type_))
     container.register(Object(42))
+    container.register(Object("42"))
 
     async with container.context() as ctx:
-        instance = await ctx.resolve(WithGenericDependency[int])
-        assert isinstance(instance, WithGenericDependency)
+        instance = await ctx.resolve(type_)
+        assert isinstance(instance, instanceof)