diff --git a/src/PIL/SpiderImagePlugin.py b/src/PIL/SpiderImagePlugin.py
index 075073f9fe3..c83d02885ff 100644
--- a/src/PIL/SpiderImagePlugin.py
+++ b/src/PIL/SpiderImagePlugin.py
@@ -211,26 +211,27 @@ def tkPhotoImage(self) -> ImageTk.PhotoImage:
 
 
 # given a list of filenames, return a list of images
-def loadImageSeries(filelist: list[str] | None = None) -> list[SpiderImageFile] | None:
+def loadImageSeries(filelist: list[str] | None = None) -> list[Image.Image] | None:
     """create a list of :py:class:`~PIL.Image.Image` objects for use in a montage"""
     if filelist is None or len(filelist) < 1:
         return None
 
-    imglist = []
+    byte_imgs = []
     for img in filelist:
         if not os.path.exists(img):
             print(f"unable to find {img}")
             continue
         try:
             with Image.open(img) as im:
-                im = im.convert2byte()
+                assert isinstance(im, SpiderImageFile)
+                byte_im = im.convert2byte()
         except Exception:
             if not isSpiderImage(img):
                 print(f"{img} is not a Spider image file")
             continue
-        im.info["filename"] = img
-        imglist.append(im)
-    return imglist
+        byte_im.info["filename"] = img
+        byte_imgs.append(byte_im)
+    return byte_imgs
 
 
 # --------------------------------------------------------------------