diff --git a/backend/chainlit/server.py b/backend/chainlit/server.py
index 64f48490b1..a980fae605 100644
--- a/backend/chainlit/server.py
+++ b/backend/chainlit/server.py
@@ -961,7 +961,7 @@ async def get_logo(theme: Optional[Theme] = Query(Theme.light)):
 @router.get("/avatars/{avatar_id:str}")
 async def get_avatar(avatar_id: str):
     """Get the avatar for the user based on the avatar_id."""
-    if not re.match(r"^[a-zA-Z0-9_ -]+$", avatar_id):
+    if not re.match(r"^[a-zA-Z0-9_-]+$", avatar_id):
         raise HTTPException(status_code=400, detail="Invalid avatar_id")
 
     if avatar_id == "default":
diff --git a/backend/tests/test_server.py b/backend/tests/test_server.py
index 91b152030f..6e98bca782 100644
--- a/backend/tests/test_server.py
+++ b/backend/tests/test_server.py
@@ -174,24 +174,6 @@ def test_get_avatar_custom(test_client: TestClient, monkeypatch: pytest.MonkeyPa
     os.remove(custom_avatar_path)
 
 
-def test_get_avatar_with_spaces(
-    test_client: TestClient, monkeypatch: pytest.MonkeyPatch
-):
-    """Test with custom avatar."""
-    custom_avatar_path = os.path.join(APP_ROOT, "public", "avatars", "my_assistant.png")
-    os.makedirs(os.path.dirname(custom_avatar_path), exist_ok=True)
-    with open(custom_avatar_path, "wb") as f:
-        f.write(b"fake image data")
-
-    response = test_client.get("/avatars/My Assistant")
-    assert response.status_code == 200
-    assert response.headers["content-type"].startswith("image/")
-    assert response.content == b"fake image data"
-
-    # Clean up
-    os.remove(custom_avatar_path)
-
-
 def test_get_avatar_non_existent_favicon(
     test_client: TestClient, monkeypatch: pytest.MonkeyPatch
 ):