diff --git a/.ci/install.sh b/.ci/install.sh
index d065e7ab5..acb84f046 100755
--- a/.ci/install.sh
+++ b/.ci/install.sh
@@ -66,7 +66,7 @@ if [[ $(uname) != CYGWIN* ]]; then
     pushd depends && ./install_raqm.sh && popd
 
     # libavif
-    pushd depends && CMAKE_POLICY_VERSION_MINIMUM=3.5 ./install_libavif.sh && popd
+    pushd depends && ./install_libavif.sh && popd
 
     # extra test images
     pushd depends && ./install_extra_test_images.sh && popd
diff --git a/.github/workflows/wheels-dependencies.sh b/.github/workflows/wheels-dependencies.sh
index a6b52064c..1583435c1 100755
--- a/.github/workflows/wheels-dependencies.sh
+++ b/.github/workflows/wheels-dependencies.sh
@@ -39,7 +39,7 @@ ARCHIVE_SDIR=pillow-depends-main
 # Package versions for fresh source builds
 FREETYPE_VERSION=2.13.3
 HARFBUZZ_VERSION=11.2.1
-LIBPNG_VERSION=1.6.47
+LIBPNG_VERSION=1.6.48
 JPEGTURBO_VERSION=3.1.0
 OPENJPEG_VERSION=2.5.3
 XZ_VERSION=5.8.1
diff --git a/Tests/helper.py b/Tests/helper.py
index 909fff879..ec61cd263 100644
--- a/Tests/helper.py
+++ b/Tests/helper.py
@@ -161,6 +161,12 @@ def assert_tuple_approx_equal(
             pytest.fail(msg + ": " + repr(actuals) + " != " + repr(targets))
 
 
+def timeout_unless_slower_valgrind(timeout: float) -> pytest.MarkDecorator:
+    if "PILLOW_VALGRIND_TEST" in os.environ:
+        return pytest.mark.pil_noop_mark()
+    return pytest.mark.timeout(timeout)
+
+
 def skip_unless_feature(feature: str) -> pytest.MarkDecorator:
     reason = f"{feature} not available"
     return pytest.mark.skipif(not features.check(feature), reason=reason)
diff --git a/Tests/test_file_eps.py b/Tests/test_file_eps.py
index b484a8cfa..d94de7287 100644
--- a/Tests/test_file_eps.py
+++ b/Tests/test_file_eps.py
@@ -15,6 +15,7 @@ from .helper import (
     is_win32,
     mark_if_feature_version,
     skip_unless_feature,
+    timeout_unless_slower_valgrind,
 )
 
 HAS_GHOSTSCRIPT = EpsImagePlugin.has_ghostscript()
@@ -398,7 +399,7 @@ def test_emptyline() -> None:
     assert image.format == "EPS"
 
 
-@pytest.mark.timeout(timeout=5)
+@timeout_unless_slower_valgrind(5)
 @pytest.mark.parametrize(
     "test_file",
     ["Tests/images/eps/timeout-d675703545fee17acab56e5fec644c19979175de.eps"],
diff --git a/Tests/test_file_fli.py b/Tests/test_file_fli.py
index 81df1ab0b..0fadd01d0 100644
--- a/Tests/test_file_fli.py
+++ b/Tests/test_file_fli.py
@@ -7,7 +7,12 @@ import pytest
 
 from PIL import FliImagePlugin, Image, ImageFile
 
-from .helper import assert_image_equal, assert_image_equal_tofile, is_pypy
+from .helper import (
+    assert_image_equal,
+    assert_image_equal_tofile,
+    is_pypy,
+    timeout_unless_slower_valgrind,
+)
 
 # created as an export of a palette image from Gimp2.6
 # save as...-> hopper.fli, default options.
@@ -189,7 +194,7 @@ def test_seek() -> None:
         "Tests/images/timeout-bff0a9dc7243a8e6ede2408d2ffa6a9964698b87.fli",
     ],
 )
-@pytest.mark.timeout(timeout=3)
+@timeout_unless_slower_valgrind(3)
 def test_timeouts(test_file: str) -> None:
     with open(test_file, "rb") as f:
         with Image.open(f) as im:
diff --git a/Tests/test_file_jpeg.py b/Tests/test_file_jpeg.py
index 7c33c7517..b9eec591d 100644
--- a/Tests/test_file_jpeg.py
+++ b/Tests/test_file_jpeg.py
@@ -32,6 +32,7 @@ from .helper import (
     is_win32,
     mark_if_feature_version,
     skip_unless_feature,
+    timeout_unless_slower_valgrind,
 )
 
 ElementTree: ModuleType | None
@@ -1033,10 +1034,7 @@ class TestFileJpeg:
         with pytest.raises(ValueError):
             im.save(f, xmp=b"1" * 65505)
 
-    @pytest.mark.timeout(timeout=1)
-    @pytest.mark.xfail(
-        "PILLOW_VALGRIND_TEST" in os.environ, reason="Valgrind is slower"
-    )
+    @timeout_unless_slower_valgrind(1)
     def test_eof(self, monkeypatch: pytest.MonkeyPatch) -> None:
         # Even though this decoder never says that it is finished
         # the image should still end when there is no new data
diff --git a/Tests/test_file_pdf.py b/Tests/test_file_pdf.py
index bde1e3ab8..a2218673b 100644
--- a/Tests/test_file_pdf.py
+++ b/Tests/test_file_pdf.py
@@ -13,7 +13,12 @@ import pytest
 
 from PIL import Image, PdfParser, features
 
-from .helper import hopper, mark_if_feature_version, skip_unless_feature
+from .helper import (
+    hopper,
+    mark_if_feature_version,
+    skip_unless_feature,
+    timeout_unless_slower_valgrind,
+)
 
 
 def helper_save_as_pdf(tmp_path: Path, mode: str, **kwargs: Any) -> str:
@@ -339,8 +344,7 @@ def test_pdf_append_to_bytesio() -> None:
     assert len(f.getvalue()) > initial_size
 
 
-@pytest.mark.timeout(1)
-@pytest.mark.skipif("PILLOW_VALGRIND_TEST" in os.environ, reason="Valgrind is slower")
+@timeout_unless_slower_valgrind(1)
 @pytest.mark.parametrize("newline", (b"\r", b"\n"))
 def test_redos(newline: bytes) -> None:
     malicious = b" trailer<<>>" + newline * 3456
diff --git a/Tests/test_file_tiff.py b/Tests/test_file_tiff.py
index b6985b83b..d0d394aa9 100644
--- a/Tests/test_file_tiff.py
+++ b/Tests/test_file_tiff.py
@@ -26,6 +26,7 @@ from .helper import (
     hopper,
     is_pypy,
     is_win32,
+    timeout_unless_slower_valgrind,
 )
 
 ElementTree: ModuleType | None
@@ -988,11 +989,8 @@ class TestFileTiff:
             with pytest.raises(OSError):
                 im.load()
 
-    @pytest.mark.timeout(6)
+    @timeout_unless_slower_valgrind(6)
     @pytest.mark.filterwarnings("ignore:Truncated File Read")
-    @pytest.mark.xfail(
-        "PILLOW_VALGRIND_TEST" in os.environ, reason="Valgrind is slower"
-    )
     def test_timeout(self, monkeypatch: pytest.MonkeyPatch) -> None:
         with Image.open("Tests/images/timeout-6646305047838720") as im:
             monkeypatch.setattr(ImageFile, "LOAD_TRUNCATED_IMAGES", True)
@@ -1004,10 +1002,7 @@ class TestFileTiff:
             "Tests/images/oom-225817ca0f8c663be7ab4b9e717b02c661e66834.tif",
         ],
     )
-    @pytest.mark.timeout(2)
-    @pytest.mark.xfail(
-        "PILLOW_VALGRIND_TEST" in os.environ, reason="Valgrind is slower"
-    )
+    @timeout_unless_slower_valgrind(2)
     def test_oom(self, test_file: str) -> None:
         with pytest.raises(UnidentifiedImageError):
             with pytest.warns(UserWarning):
diff --git a/Tests/test_image.py b/Tests/test_image.py
index 7e6118d52..14a067127 100644
--- a/Tests/test_image.py
+++ b/Tests/test_image.py
@@ -34,6 +34,7 @@ from .helper import (
     is_win32,
     mark_if_feature_version,
     skip_unless_feature,
+    timeout_unless_slower_valgrind,
 )
 
 ElementTree: ModuleType | None
@@ -572,10 +573,7 @@ class TestImage:
         i = Image.new("RGB", [1, 1])
         assert isinstance(i.size, tuple)
 
-    @pytest.mark.timeout(0.75)
-    @pytest.mark.skipif(
-        "PILLOW_VALGRIND_TEST" in os.environ, reason="Valgrind is slower"
-    )
+    @timeout_unless_slower_valgrind(0.75)
     @pytest.mark.parametrize("size", ((0, 100000000), (100000000, 0)))
     def test_empty_image(self, size: tuple[int, int]) -> None:
         Image.new("RGB", size)
diff --git a/Tests/test_imagefontpil.py b/Tests/test_imagefontpil.py
index e5b770745..3eb98d379 100644
--- a/Tests/test_imagefontpil.py
+++ b/Tests/test_imagefontpil.py
@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-import os
 import struct
 from io import BytesIO
 
@@ -8,7 +7,7 @@ import pytest
 
 from PIL import Image, ImageDraw, ImageFont, _util, features
 
-from .helper import assert_image_equal_tofile
+from .helper import assert_image_equal_tofile, timeout_unless_slower_valgrind
 
 fonts = [ImageFont.load_default_imagefont()]
 if not features.check_module("freetype2"):
@@ -73,8 +72,7 @@ def test_decompression_bomb() -> None:
         font.getmask("A" * 1_000_000)
 
 
-@pytest.mark.timeout(4)
-@pytest.mark.xfail("PILLOW_VALGRIND_TEST" in os.environ, reason="Valgrind is slower")
+@timeout_unless_slower_valgrind(4)
 def test_oom() -> None:
     glyph = struct.pack(
         ">hhhhhhhhhh", 1, 0, -32767, -32767, 32767, 32767, -32767, -32767, 32767, 32767
diff --git a/setup.py b/setup.py
index 5d41e27d9..ab36c6b17 100644
--- a/setup.py
+++ b/setup.py
@@ -224,13 +224,14 @@ def _add_directory(
         path.insert(where, subdir)
 
 
-def _find_include_file(self: pil_build_ext, include: str) -> int:
+def _find_include_file(self: pil_build_ext, include: str) -> str | None:
     for directory in self.compiler.include_dirs:
         _dbg("Checking for include file %s in %s", (include, directory))
-        if os.path.isfile(os.path.join(directory, include)):
+        path = os.path.join(directory, include)
+        if os.path.isfile(path):
             _dbg("Found %s", include)
-            return 1
-    return 0
+            return path
+    return None
 
 
 def _find_library_file(self: pil_build_ext, library: str) -> str | None:
@@ -852,9 +853,13 @@ class pil_build_ext(build_ext):
 
         if feature.want("avif"):
             _dbg("Looking for avif")
-            if _find_include_file(self, "avif/avif.h"):
-                if _find_library_file(self, "avif"):
-                    feature.set("avif", "avif")
+            if avif_h := _find_include_file(self, "avif/avif.h"):
+                with open(avif_h, "rb") as fp:
+                    major_version = int(
+                        fp.read().split(b"#define AVIF_VERSION_MAJOR ")[1].split()[0]
+                    )
+                    if major_version >= 1 and _find_library_file(self, "avif"):
+                        feature.set("avif", "avif")
 
         for f in feature:
             if not feature.get(f) and feature.require(f):
diff --git a/src/PIL/WmfImagePlugin.py b/src/PIL/WmfImagePlugin.py
index f709d026b..d569cb4b8 100644
--- a/src/PIL/WmfImagePlugin.py
+++ b/src/PIL/WmfImagePlugin.py
@@ -81,7 +81,7 @@ class WmfStubImageFile(ImageFile.StubImageFile):
 
     def _open(self) -> None:
         # check placable header
-        s = self.fp.read(80)
+        s = self.fp.read(44)
 
         if s.startswith(b"\xd7\xcd\xc6\x9a\x00\x00"):
             # placeable windows metafile
diff --git a/winbuild/build_prepare.py b/winbuild/build_prepare.py
index d23f0eb5b..6e176e29c 100644
--- a/winbuild/build_prepare.py
+++ b/winbuild/build_prepare.py
@@ -118,7 +118,7 @@ V = {
     "LCMS2": "2.17",
     "LIBAVIF": "1.3.0",
     "LIBIMAGEQUANT": "4.3.4",
-    "LIBPNG": "1.6.47",
+    "LIBPNG": "1.6.48",
     "LIBWEBP": "1.5.0",
     "OPENJPEG": "2.5.3",
     "TIFF": "4.7.0",