diff --git a/ninja/testing/client.py b/ninja/testing/client.py
index 0be8ce0a..00e78d3f 100644
--- a/ninja/testing/client.py
+++ b/ninja/testing/client.py
@@ -26,7 +26,12 @@ def build_absolute_uri(location: Optional[str] = None) -> str:
 class NinjaClientBase:
     __test__ = False  # <- skip pytest
 
-    def __init__(self, router_or_app: Union[NinjaAPI, Router]) -> None:
+    def __init__(
+        self,
+        router_or_app: Union[NinjaAPI, Router],
+        headers: Optional[Dict[str, str]] = None,
+    ) -> None:
+        self.headers = headers or {}
         self.router_or_app = router_or_app
 
     def get(
@@ -82,6 +87,11 @@ def request(
             request_params["body"] = json_dumps(json, cls=NinjaJSONEncoder)
         if data is None:
             data = {}
+        if self.headers or request_params.get("headers"):
+            request_params["headers"] = {
+                **self.headers,
+                **request_params.get("headers", {}),
+            }
         func, request, kwargs = self._resolve(method, path, data, request_params)
         return self._call(func, request, kwargs)  # type: ignore
 
diff --git a/tests/test_test_client.py b/tests/test_test_client.py
index 67f15e72..e182c20e 100644
--- a/tests/test_test_client.py
+++ b/tests/test_test_client.py
@@ -27,6 +27,11 @@ def simple_get(request):
     return "test"
 
 
+@router.get("/test-headers")
+def get_headers(request):
+    return dict(request.headers)
+
+
 client = TestClient(router)
 
 
@@ -78,3 +83,21 @@ def test_json_as_body():
             ClientTestSchema.model_validate_json(request.body).model_dump_json()
             == schema_instance.model_dump_json()
         )
+
+
+headered_client = TestClient(router, headers={"A": "a", "B": "b"})
+
+
+def test_client_request_only_header():
+    r = client.get("/test-headers", headers={"A": "na"})
+    assert r.json() == {"A": "na"}
+
+
+def test_headered_client_request_with_default_headers():
+    r = headered_client.get("/test-headers")
+    assert r.json() == {"A": "a", "B": "b"}
+
+
+def test_headered_client_request_with_overwritten_and_additional_headers():
+    r = headered_client.get("/test-headers", headers={"A": "na", "C": "nc"})
+    assert r.json() == {"A": "na", "B": "b", "C": "nc"}