diff --git a/src/PIL/ImageFile.py b/src/PIL/ImageFile.py
index 14038e4732d..3c15245848e 100644
--- a/src/PIL/ImageFile.py
+++ b/src/PIL/ImageFile.py
@@ -113,7 +113,7 @@ class _Tile(NamedTuple):
 # ImageFile base class
 
 
-class ImageFile(Image.Image):
+class ImageFile(Image.Image, metaclass=abc.ABCMeta):
     """Base class for image file format handlers."""
 
     def __init__(
@@ -175,6 +175,7 @@ def __init__(
                 self.fp.close()
             raise
 
+    @abc.abstractmethod
     def _open(self) -> None:
         pass
 
@@ -480,7 +481,7 @@ def load(self, im: StubImageFile) -> Image.Image:
         pass
 
 
-class StubImageFile(ImageFile, metaclass=abc.ABCMeta):
+class StubImageFile(ImageFile):
     """
     Base class for stub image loaders.
 
@@ -490,10 +491,6 @@ class StubImageFile(ImageFile, metaclass=abc.ABCMeta):
 
     _handler: StubHandler | None = None
 
-    @abc.abstractmethod
-    def _open(self) -> None:
-        pass
-
     def load(self) -> Image.core.PixelAccess | None:
         if self._handler is None:
             msg = f"cannot find loader for this {self.format} file"