diff --git a/tiatoolbox/tools/stainnorm.py b/tiatoolbox/tools/stainnorm.py
index 755c28d22..bad835236 100644
--- a/tiatoolbox/tools/stainnorm.py
+++ b/tiatoolbox/tools/stainnorm.py
@@ -367,13 +367,7 @@ def get_mean_std(
 def get_normalizer(
     method_name: str,
     stain_matrix: np.ndarray | None = None,
-) -> (
-    ReinhardNormalizer
-    | RuifrokNormalizer
-    | MacenkoNormalizer
-    | VahadaneNormalizer
-    | CustomNormalizer
-):
+) -> StainNormalizer:
     """Return a :class:`.StainNormalizer` with corresponding name.
 
     Args: