diff --git a/Tests/test_file_bufrstub.py b/Tests/test_file_bufrstub.py
index 362578c56ef..8c6bb1a69f7 100644
--- a/Tests/test_file_bufrstub.py
+++ b/Tests/test_file_bufrstub.py
@@ -61,6 +61,7 @@ def open(self, im: ImageFile.StubImageFile) -> None:
 
         def load(self, im: ImageFile.StubImageFile) -> Image.Image:
             self.loaded = True
+            assert im.fp is not None
             im.fp.close()
             return Image.new("RGB", (1, 1))
 
diff --git a/Tests/test_file_gribstub.py b/Tests/test_file_gribstub.py
index 4dbed6b3190..05925d50202 100644
--- a/Tests/test_file_gribstub.py
+++ b/Tests/test_file_gribstub.py
@@ -61,6 +61,7 @@ def open(self, im: Image.Image) -> None:
 
         def load(self, im: ImageFile.ImageFile) -> Image.Image:
             self.loaded = True
+            assert im.fp is not None
             im.fp.close()
             return Image.new("RGB", (1, 1))
 
diff --git a/Tests/test_file_hdf5stub.py b/Tests/test_file_hdf5stub.py
index 1e48597d366..e1a56309b90 100644
--- a/Tests/test_file_hdf5stub.py
+++ b/Tests/test_file_hdf5stub.py
@@ -63,6 +63,7 @@ def open(self, im: Image.Image) -> None:
 
         def load(self, im: ImageFile.ImageFile) -> Image.Image:
             self.loaded = True
+            assert im.fp is not None
             im.fp.close()
             return Image.new("RGB", (1, 1))
 
diff --git a/Tests/test_file_jpeg.py b/Tests/test_file_jpeg.py
index 96e7f4239b8..f818927f6a3 100644
--- a/Tests/test_file_jpeg.py
+++ b/Tests/test_file_jpeg.py
@@ -1133,8 +1133,9 @@ def test_fd_leak(self, tmp_path: Path) -> None:
             im.save(tmpfile)
 
         im = Image.open(tmpfile)
+        assert im.fp is not None
+        assert not im.fp.closed
         fp = im.fp
-        assert not fp.closed
         with pytest.raises(OSError):
             os.remove(tmpfile)
         im.load()
diff --git a/Tests/test_file_libtiff.py b/Tests/test_file_libtiff.py
index e36b5f39e3c..46c244658c3 100644
--- a/Tests/test_file_libtiff.py
+++ b/Tests/test_file_libtiff.py
@@ -610,8 +610,9 @@ def test_bw_compression_w_rgb(self, compression: str, tmp_path: Path) -> None:
             im.save(out, compression=compression)
 
     def test_fp_leak(self) -> None:
-        im: Image.Image | None = Image.open("Tests/images/hopper_g4_500.tif")
+        im: ImageFile.ImageFile | None = Image.open("Tests/images/hopper_g4_500.tif")
         assert im is not None
+        assert im.fp is not None
         fn = im.fp.fileno()
 
         os.fstat(fn)
diff --git a/Tests/test_file_tiff.py b/Tests/test_file_tiff.py
index 556c886476e..c6c8467d629 100644
--- a/Tests/test_file_tiff.py
+++ b/Tests/test_file_tiff.py
@@ -971,6 +971,7 @@ def test_close_on_load_exclusive(self, tmp_path: Path) -> None:
 
         im = Image.open(tmpfile)
         fp = im.fp
+        assert fp is not None
         assert not fp.closed
         im.load()
         assert fp.closed
@@ -984,6 +985,7 @@ def test_close_on_load_nonexclusive(self, tmp_path: Path) -> None:
         with open(tmpfile, "rb") as f:
             im = Image.open(f)
             fp = im.fp
+            assert fp is not None
             assert not fp.closed
             im.load()
             assert not fp.closed
@@ -1034,8 +1036,9 @@ def test_fd_leak(self, tmp_path: Path) -> None:
             im.save(tmpfile)
 
         im = Image.open(tmpfile)
+        assert im.fp is not None
+        assert not im.fp.closed
         fp = im.fp
-        assert not fp.closed
         with pytest.raises(OSError):
             os.remove(tmpfile)
         im.load()
diff --git a/Tests/test_image_load.py b/Tests/test_image_load.py
index 4f1d63b8f43..1d5f0d17cd6 100644
--- a/Tests/test_image_load.py
+++ b/Tests/test_image_load.py
@@ -38,6 +38,7 @@ def test_close_after_load(caplog: pytest.LogCaptureFixture) -> None:
 def test_contextmanager() -> None:
     fn = None
     with Image.open("Tests/images/hopper.gif") as im:
+        assert im.fp is not None
         fn = im.fp.fileno()
         os.fstat(fn)
 
diff --git a/docs/example/DdsImagePlugin.py b/docs/example/DdsImagePlugin.py
index e4b6b9c01b6..e0557976c28 100644
--- a/docs/example/DdsImagePlugin.py
+++ b/docs/example/DdsImagePlugin.py
@@ -213,6 +213,7 @@ class DdsImageFile(ImageFile.ImageFile):
     format_description = "DirectDraw Surface"
 
     def _open(self) -> None:
+        assert self.fp is not None
         if not _accept(self.fp.read(4)):
             msg = "not a DDS file"
             raise SyntaxError(msg)
diff --git a/src/PIL/AvifImagePlugin.py b/src/PIL/AvifImagePlugin.py
index 366e0c864bf..43c39a9fbe7 100644
--- a/src/PIL/AvifImagePlugin.py
+++ b/src/PIL/AvifImagePlugin.py
@@ -77,6 +77,8 @@ def _open(self) -> None:
         ):
             msg = "Invalid opening codec"
             raise ValueError(msg)
+
+        assert self.fp is not None
         self._decoder = _avif.AvifDecoder(
             self.fp.read(),
             DECODE_CODEC_CHOICE,
diff --git a/src/PIL/BlpImagePlugin.py b/src/PIL/BlpImagePlugin.py
index f7be7746d84..6bb92edf891 100644
--- a/src/PIL/BlpImagePlugin.py
+++ b/src/PIL/BlpImagePlugin.py
@@ -258,6 +258,7 @@ class BlpImageFile(ImageFile.ImageFile):
     format_description = "Blizzard Mipmap Format"
 
     def _open(self) -> None:
+        assert self.fp is not None
         self.magic = self.fp.read(4)
         if not _accept(self.magic):
             msg = f"Bad BLP magic {repr(self.magic)}"
diff --git a/src/PIL/BmpImagePlugin.py b/src/PIL/BmpImagePlugin.py
index 54fc69ab454..a1227137017 100644
--- a/src/PIL/BmpImagePlugin.py
+++ b/src/PIL/BmpImagePlugin.py
@@ -76,6 +76,7 @@ class BmpImageFile(ImageFile.ImageFile):
 
     def _bitmap(self, header: int = 0, offset: int = 0) -> None:
         """Read relevant info about the BMP"""
+        assert self.fp is not None
         read, seek = self.fp.read, self.fp.seek
         if header:
             seek(header)
@@ -311,6 +312,7 @@ def _bitmap(self, header: int = 0, offset: int = 0) -> None:
     def _open(self) -> None:
         """Open file, check magic number and read header"""
         # read 14 bytes: magic number, filesize, reserved, header final offset
+        assert self.fp is not None
         head_data = self.fp.read(14)
         # choke if the file does not have the required magic bytes
         if not _accept(head_data):
diff --git a/src/PIL/BufrStubImagePlugin.py b/src/PIL/BufrStubImagePlugin.py
index 8c5da14f5f6..264564d2bbb 100644
--- a/src/PIL/BufrStubImagePlugin.py
+++ b/src/PIL/BufrStubImagePlugin.py
@@ -41,6 +41,7 @@ class BufrStubImageFile(ImageFile.StubImageFile):
     format_description = "BUFR"
 
     def _open(self) -> None:
+        assert self.fp is not None
         if not _accept(self.fp.read(4)):
             msg = "Not a BUFR file"
             raise SyntaxError(msg)
diff --git a/src/PIL/DcxImagePlugin.py b/src/PIL/DcxImagePlugin.py
index aea661b9cb6..d3f456ddcc4 100644
--- a/src/PIL/DcxImagePlugin.py
+++ b/src/PIL/DcxImagePlugin.py
@@ -45,6 +45,7 @@ class DcxImageFile(PcxImageFile):
 
     def _open(self) -> None:
         # Header
+        assert self.fp is not None
         s = self.fp.read(4)
         if not _accept(s):
             msg = "not a DCX file"
diff --git a/src/PIL/EpsImagePlugin.py b/src/PIL/EpsImagePlugin.py
index 69f3062b4d4..2effb816cfb 100644
--- a/src/PIL/EpsImagePlugin.py
+++ b/src/PIL/EpsImagePlugin.py
@@ -189,6 +189,7 @@ class EpsImageFile(ImageFile.ImageFile):
     mode_map = {1: "L", 2: "LAB", 3: "RGB", 4: "CMYK"}
 
     def _open(self) -> None:
+        assert self.fp is not None
         (length, offset) = self._find_offset(self.fp)
 
         # go to offset - start of "%!PS"
@@ -403,6 +404,7 @@ def load(
     ) -> Image.core.PixelAccess | None:
         # Load EPS via Ghostscript
         if self.tile:
+            assert self.fp is not None
             self.im = Ghostscript(self.tile, self.size, self.fp, scale, transparency)
             self._mode = self.im.mode
             self._size = self.im.size
diff --git a/src/PIL/FpxImagePlugin.py b/src/PIL/FpxImagePlugin.py
index fd992cd9e20..297971234d8 100644
--- a/src/PIL/FpxImagePlugin.py
+++ b/src/PIL/FpxImagePlugin.py
@@ -58,6 +58,7 @@ def _open(self) -> None:
         # read the OLE directory and see if this is a likely
         # to be a FlashPix file
 
+        assert self.fp is not None
         try:
             self.ole = olefile.OleFileIO(self.fp)
         except OSError as e:
@@ -229,6 +230,7 @@ def _open_subimage(self, index: int = 1, subimage: int = 0) -> None:
                 if y >= ysize:
                     break  # isn't really required
 
+        assert self.fp is not None
         self.stream = stream
         self._fp = self.fp
         self.fp = None
diff --git a/src/PIL/FtexImagePlugin.py b/src/PIL/FtexImagePlugin.py
index d60e75bb60b..e4d836cbdb2 100644
--- a/src/PIL/FtexImagePlugin.py
+++ b/src/PIL/FtexImagePlugin.py
@@ -72,6 +72,7 @@ class FtexImageFile(ImageFile.ImageFile):
     format_description = "Texture File Format (IW2:EOC)"
 
     def _open(self) -> None:
+        assert self.fp is not None
         if not _accept(self.fp.read(4)):
             msg = "not an FTEX file"
             raise SyntaxError(msg)
diff --git a/src/PIL/GbrImagePlugin.py b/src/PIL/GbrImagePlugin.py
index d69295363f3..ec666c81c2c 100644
--- a/src/PIL/GbrImagePlugin.py
+++ b/src/PIL/GbrImagePlugin.py
@@ -42,6 +42,7 @@ class GbrImageFile(ImageFile.ImageFile):
     format_description = "GIMP brush file"
 
     def _open(self) -> None:
+        assert self.fp is not None
         header_size = i32(self.fp.read(4))
         if header_size < 20:
             msg = "not a GIMP brush"
@@ -88,6 +89,7 @@ def _open(self) -> None:
 
     def load(self) -> Image.core.PixelAccess | None:
         if self._im is None:
+            assert self.fp is not None
             self.im = Image.core.new(self.mode, self.size)
             self.frombytes(self.fp.read(self._data_size))
         return Image.Image.load(self)
diff --git a/src/PIL/GifImagePlugin.py b/src/PIL/GifImagePlugin.py
index 0560a5a7dc8..b8755422d05 100644
--- a/src/PIL/GifImagePlugin.py
+++ b/src/PIL/GifImagePlugin.py
@@ -87,6 +87,7 @@ class GifImageFile(ImageFile.ImageFile):
     global_palette = None
 
     def data(self) -> bytes | None:
+        assert self.fp is not None
         s = self.fp.read(1)
         if s and s[0]:
             return self.fp.read(s[0])
@@ -100,6 +101,7 @@ def _is_palette_needed(self, p: bytes) -> bool:
 
     def _open(self) -> None:
         # Screen
+        assert self.fp is not None
         s = self.fp.read(13)
         if not _accept(s):
             msg = "not a GIF file"
diff --git a/src/PIL/GribStubImagePlugin.py b/src/PIL/GribStubImagePlugin.py
index dfa798893cb..146a6fa0df0 100644
--- a/src/PIL/GribStubImagePlugin.py
+++ b/src/PIL/GribStubImagePlugin.py
@@ -41,6 +41,7 @@ class GribStubImageFile(ImageFile.StubImageFile):
     format_description = "GRIB"
 
     def _open(self) -> None:
+        assert self.fp is not None
         if not _accept(self.fp.read(8)):
             msg = "Not a GRIB file"
             raise SyntaxError(msg)
diff --git a/src/PIL/Hdf5StubImagePlugin.py b/src/PIL/Hdf5StubImagePlugin.py
index 76e640f15ab..1523e95d58c 100644
--- a/src/PIL/Hdf5StubImagePlugin.py
+++ b/src/PIL/Hdf5StubImagePlugin.py
@@ -41,6 +41,7 @@ class HDF5StubImageFile(ImageFile.StubImageFile):
     format_description = "HDF5"
 
     def _open(self) -> None:
+        assert self.fp is not None
         if not _accept(self.fp.read(8)):
             msg = "Not an HDF file"
             raise SyntaxError(msg)
diff --git a/src/PIL/IcnsImagePlugin.py b/src/PIL/IcnsImagePlugin.py
index 197ea7a2bb2..058861d67e5 100644
--- a/src/PIL/IcnsImagePlugin.py
+++ b/src/PIL/IcnsImagePlugin.py
@@ -265,6 +265,7 @@ class IcnsImageFile(ImageFile.ImageFile):
     format_description = "Mac OS icns resource"
 
     def _open(self) -> None:
+        assert self.fp is not None
         self.icns = IcnsFile(self.fp)
         self._mode = "RGBA"
         self.info["sizes"] = self.icns.itersizes()
diff --git a/src/PIL/IcoImagePlugin.py b/src/PIL/IcoImagePlugin.py
index d5da07d470c..8dd57ff858a 100644
--- a/src/PIL/IcoImagePlugin.py
+++ b/src/PIL/IcoImagePlugin.py
@@ -340,6 +340,7 @@ class IcoImageFile(ImageFile.ImageFile):
     format_description = "Windows Icon"
 
     def _open(self) -> None:
+        assert self.fp is not None
         self.ico = IcoFile(self.fp)
         self.info["sizes"] = self.ico.sizes()
         self.size = self.ico.entry[0].dim
diff --git a/src/PIL/ImImagePlugin.py b/src/PIL/ImImagePlugin.py
index 71b9996780c..ef54f16e97e 100644
--- a/src/PIL/ImImagePlugin.py
+++ b/src/PIL/ImImagePlugin.py
@@ -125,6 +125,7 @@ def _open(self) -> None:
         # Quick rejection: if there's not an LF among the first
         # 100 bytes, this is (probably) not a text header.
 
+        assert self.fp is not None
         if b"\n" not in self.fp.read(100):
             msg = "not an IM file"
             raise SyntaxError(msg)
diff --git a/src/PIL/Image.py b/src/PIL/Image.py
index b71395c6234..4e61900f6fd 100644
--- a/src/PIL/Image.py
+++ b/src/PIL/Image.py
@@ -1524,6 +1524,8 @@ def getexif(self) -> Exif:
                 assert isinstance(self, TiffImagePlugin.TiffImageFile)
                 self._exif.bigtiff = self.tag_v2._bigtiff
                 self._exif.endian = self.tag_v2._endian
+
+                assert self.fp is not None
                 self._exif.load_from_fp(self.fp, self.tag_v2._offset)
         if exif_info is not None:
             self._exif.load(exif_info)
diff --git a/src/PIL/ImageFile.py b/src/PIL/ImageFile.py
index a1d98bd5103..c2588c3dd70 100644
--- a/src/PIL/ImageFile.py
+++ b/src/PIL/ImageFile.py
@@ -285,6 +285,7 @@ def load(self) -> Image.core.PixelAccess | None:
         self.map: mmap.mmap | None = None
         use_mmap = self.filename and len(self.tile) == 1
 
+        assert self.fp is not None
         readonly = 0
 
         # look for read/seek overrides
diff --git a/src/PIL/IptcImagePlugin.py b/src/PIL/IptcImagePlugin.py
index c28f4dcc797..e63c652539e 100644
--- a/src/PIL/IptcImagePlugin.py
+++ b/src/PIL/IptcImagePlugin.py
@@ -49,6 +49,7 @@ def getint(self, key: tuple[int, int]) -> int:
     def field(self) -> tuple[tuple[int, int] | None, int]:
         #
         # get a IPTC field header
+        assert self.fp is not None
         s = self.fp.read(5)
         if not s.strip(b"\x00"):
             return None, 0
@@ -76,6 +77,7 @@ def field(self) -> tuple[tuple[int, int] | None, int]:
 
     def _open(self) -> None:
         # load descriptive fields
+        assert self.fp is not None
         while True:
             offset = self.fp.tell()
             tag, size = self.field()
@@ -131,6 +133,7 @@ def load(self) -> Image.core.PixelAccess | None:
             assert isinstance(args, tuple)
             compression, band = args
 
+            assert self.fp is not None
             self.fp.seek(self.tile[0].offset)
 
             # Copy image data to temporary file
diff --git a/src/PIL/Jpeg2KImagePlugin.py b/src/PIL/Jpeg2KImagePlugin.py
index 4c85dd4e281..d6ec38d4310 100644
--- a/src/PIL/Jpeg2KImagePlugin.py
+++ b/src/PIL/Jpeg2KImagePlugin.py
@@ -252,6 +252,7 @@ class Jpeg2KImageFile(ImageFile.ImageFile):
     format_description = "JPEG 2000 (ISO 15444)"
 
     def _open(self) -> None:
+        assert self.fp is not None
         sig = self.fp.read(4)
         if sig == b"\xff\x4f\xff\x51":
             self.codec = "j2k"
@@ -304,6 +305,7 @@ def _open(self) -> None:
         ]
 
     def _parse_comment(self) -> None:
+        assert self.fp is not None
         while True:
             marker = self.fp.read(2)
             if not marker:
diff --git a/src/PIL/JpegImagePlugin.py b/src/PIL/JpegImagePlugin.py
index 755ca648e55..894c1547d7b 100644
--- a/src/PIL/JpegImagePlugin.py
+++ b/src/PIL/JpegImagePlugin.py
@@ -61,6 +61,7 @@
 
 
 def Skip(self: JpegImageFile, marker: int) -> None:
+    assert self.fp is not None
     n = i16(self.fp.read(2)) - 2
     ImageFile._safe_read(self.fp, n)
 
@@ -70,6 +71,7 @@ def APP(self: JpegImageFile, marker: int) -> None:
     # Application marker.  Store these in the APP dictionary.
     # Also look for well-known application markers.
 
+    assert self.fp is not None
     n = i16(self.fp.read(2)) - 2
     s = ImageFile._safe_read(self.fp, n)
 
@@ -174,6 +176,7 @@ def APP(self: JpegImageFile, marker: int) -> None:
 def COM(self: JpegImageFile, marker: int) -> None:
     #
     # Comment marker.  Store these in the APP dictionary.
+    assert self.fp is not None
     n = i16(self.fp.read(2)) - 2
     s = ImageFile._safe_read(self.fp, n)
 
@@ -190,6 +193,7 @@ def SOF(self: JpegImageFile, marker: int) -> None:
     # mode.  Note that this could be made a bit brighter, by
     # looking for JFIF and Adobe APP markers.
 
+    assert self.fp is not None
     n = i16(self.fp.read(2)) - 2
     s = ImageFile._safe_read(self.fp, n)
     self._size = i16(s, 3), i16(s, 1)
@@ -240,6 +244,7 @@ def DQT(self: JpegImageFile, marker: int) -> None:
     # FIXME: The quantization tables can be used to estimate the
     # compression quality.
 
+    assert self.fp is not None
     n = i16(self.fp.read(2)) - 2
     s = ImageFile._safe_read(self.fp, n)
     while len(s):
@@ -340,6 +345,7 @@ class JpegImageFile(ImageFile.ImageFile):
     format_description = "JPEG (ISO 10918)"
 
     def _open(self) -> None:
+        assert self.fp is not None
         s = self.fp.read(3)
 
         if not _accept(s):
@@ -408,6 +414,7 @@ def load_read(self, read_bytes: int) -> bytes:
         For premature EOF and LOAD_TRUNCATED_IMAGES adds EOI marker
         so libjpeg can finish decoding
         """
+        assert self.fp is not None
         s = self.fp.read(read_bytes)
 
         if not s and ImageFile.LOAD_TRUNCATED_IMAGES and not hasattr(self, "_ended"):
diff --git a/src/PIL/MicImagePlugin.py b/src/PIL/MicImagePlugin.py
index 9ce38c427b6..99a07bae02c 100644
--- a/src/PIL/MicImagePlugin.py
+++ b/src/PIL/MicImagePlugin.py
@@ -67,6 +67,7 @@ def _open(self) -> None:
         self._n_frames = len(self.images)
         self.is_animated = self._n_frames > 1
 
+        assert self.fp is not None
         self.__fp = self.fp
         self.seek(0)
 
diff --git a/src/PIL/MpoImagePlugin.py b/src/PIL/MpoImagePlugin.py
index b1ae07873ac..9360061ba18 100644
--- a/src/PIL/MpoImagePlugin.py
+++ b/src/PIL/MpoImagePlugin.py
@@ -106,6 +106,7 @@ class MpoImageFile(JpegImagePlugin.JpegImageFile):
     _close_exclusive_fp_after_loading = False
 
     def _open(self) -> None:
+        assert self.fp is not None
         self.fp.seek(0)  # prep the fp in order to pass the JPEG test
         JpegImagePlugin.JpegImageFile._open(self)
         self._after_jpeg_open()
@@ -125,6 +126,7 @@ def _after_jpeg_open(self, mpheader: dict[int, Any] | None = None) -> None:
         assert self.n_frames == len(self.__mpoffsets)
         del self.info["mpoffset"]  # no longer needed
         self.is_animated = self.n_frames > 1
+        assert self.fp is not None
         self._fp = self.fp  # FIXME: hack
         self._fp.seek(self.__mpoffsets[0])  # get ready to read first frame
         self.__frame = 0
diff --git a/src/PIL/PngImagePlugin.py b/src/PIL/PngImagePlugin.py
index 967308221ad..fae59724d73 100644
--- a/src/PIL/PngImagePlugin.py
+++ b/src/PIL/PngImagePlugin.py
@@ -759,6 +759,7 @@ class PngImageFile(ImageFile.ImageFile):
     format_description = "Portable network graphics"
 
     def _open(self) -> None:
+        assert self.fp is not None
         if not _accept(self.fp.read(8)):
             msg = "not a PNG file"
             raise SyntaxError(msg)
@@ -990,6 +991,7 @@ def load_read(self, read_bytes: int) -> bytes:
         """internal: read more image data"""
 
         assert self.png is not None
+        assert self.fp is not None
         while self.__idat == 0:
             # end of chunk, skip forward to next one
 
@@ -1023,6 +1025,7 @@ def load_read(self, read_bytes: int) -> bytes:
     def load_end(self) -> None:
         """internal: finished reading image data"""
         assert self.png is not None
+        assert self.fp is not None
         if self.__idat != 0:
             self.fp.read(self.__idat)
         while True:
diff --git a/src/PIL/PsdImagePlugin.py b/src/PIL/PsdImagePlugin.py
index f49aaeeb1f5..69a8703dd8b 100644
--- a/src/PIL/PsdImagePlugin.py
+++ b/src/PIL/PsdImagePlugin.py
@@ -61,6 +61,7 @@ class PsdImageFile(ImageFile.ImageFile):
     _close_exclusive_fp_after_loading = False
 
     def _open(self) -> None:
+        assert self.fp is not None
         read = self.fp.read
 
         #
diff --git a/src/PIL/QoiImagePlugin.py b/src/PIL/QoiImagePlugin.py
index dba5d809fef..d0709b1198a 100644
--- a/src/PIL/QoiImagePlugin.py
+++ b/src/PIL/QoiImagePlugin.py
@@ -25,6 +25,7 @@ class QoiImageFile(ImageFile.ImageFile):
     format_description = "Quite OK Image"
 
     def _open(self) -> None:
+        assert self.fp is not None
         if not _accept(self.fp.read(4)):
             msg = "not a QOI file"
             raise SyntaxError(msg)
diff --git a/src/PIL/SpiderImagePlugin.py b/src/PIL/SpiderImagePlugin.py
index 868019e80a8..b2391560b54 100644
--- a/src/PIL/SpiderImagePlugin.py
+++ b/src/PIL/SpiderImagePlugin.py
@@ -104,6 +104,7 @@ class SpiderImageFile(ImageFile.ImageFile):
     def _open(self) -> None:
         # check header
         n = 27 * 4  # read 27 float values
+        assert self.fp is not None
         f = self.fp.read(n)
 
         try:
diff --git a/src/PIL/WalImageFile.py b/src/PIL/WalImageFile.py
index 5494f62e892..fb3e1c06a32 100644
--- a/src/PIL/WalImageFile.py
+++ b/src/PIL/WalImageFile.py
@@ -39,6 +39,7 @@ def _open(self) -> None:
         self._mode = "P"
 
         # read header fields
+        assert self.fp is not None
         header = self.fp.read(32 + 24 + 32 + 12)
         self._size = i32(header, 32), i32(header, 36)
         Image._decompression_bomb_check(self.size)
@@ -54,6 +55,7 @@ def _open(self) -> None:
 
     def load(self) -> Image.core.PixelAccess | None:
         if self._im is None:
+            assert self.fp is not None
             self.im = Image.core.new(self.mode, self.size)
             self.frombytes(self.fp.read(self.size[0] * self.size[1]))
             self.putpalette(quake2palette)
diff --git a/src/PIL/WebPImagePlugin.py b/src/PIL/WebPImagePlugin.py
index 2847fed20a0..737bfe5eb6e 100644
--- a/src/PIL/WebPImagePlugin.py
+++ b/src/PIL/WebPImagePlugin.py
@@ -45,6 +45,7 @@ class WebPImageFile(ImageFile.ImageFile):
     def _open(self) -> None:
         # Use the newer AnimDecoder API to parse the (possibly) animated file,
         # and access muxed chunks like ICC/EXIF/XMP.
+        assert self.fp is not None
         self._decoder = _webp.WebPAnimDecoder(self.fp.read())
 
         # Get info from decoder
diff --git a/src/PIL/WmfImagePlugin.py b/src/PIL/WmfImagePlugin.py
index de714d33794..3ae86242a8b 100644
--- a/src/PIL/WmfImagePlugin.py
+++ b/src/PIL/WmfImagePlugin.py
@@ -49,6 +49,7 @@ def open(self, im: ImageFile.StubImageFile) -> None:
             self.bbox = im.info["wmf_bbox"]
 
         def load(self, im: ImageFile.StubImageFile) -> Image.Image:
+            assert im.fp is not None
             im.fp.seek(0)  # rewind
             return Image.frombytes(
                 "RGB",
@@ -81,6 +82,7 @@ class WmfStubImageFile(ImageFile.StubImageFile):
 
     def _open(self) -> None:
         # check placeable header
+        assert self.fp is not None
         s = self.fp.read(44)
 
         if s.startswith(b"\xd7\xcd\xc6\x9a\x00\x00"):