diff --git a/src/jpeglib/dct_jpeg.py b/src/jpeglib/dct_jpeg.py
index 761ee08..55f3382 100644
--- a/src/jpeglib/dct_jpeg.py
+++ b/src/jpeglib/dct_jpeg.py
@@ -321,7 +321,7 @@ def free(self):
         del self._K
         del self._qt
 
-    def __add__(self, delta: Tuple[np.ndarray]) -> DCTJPEG:
+    def __add__(self, delta: Tuple[np.ndarray]):
         """Add difference image (e.g., steganographic noise) to respective components.
 
         :param delta: difference images