diff --git a/Tests/oss-fuzz/build.sh b/Tests/oss-fuzz/build.sh
index 37fad7bc8..3aa6c7f6a 100755
--- a/Tests/oss-fuzz/build.sh
+++ b/Tests/oss-fuzz/build.sh
@@ -15,7 +15,7 @@
 #
 ################################################################################
 
-python3 setup.py build --build-base=/tmp/build install
+python3 -m pip install .
 
 # Build fuzzers in $OUT.
 for fuzzer in $(find $SRC -name 'fuzz_*.py'); do
diff --git a/Tests/test_imageops.py b/Tests/test_imageops.py
index 6d153ccea..a3bb536ce 100644
--- a/Tests/test_imageops.py
+++ b/Tests/test_imageops.py
@@ -433,6 +433,12 @@ def test_exif_transpose_in_place():
         assert_image_equal(im, expected)
 
 
+def test_autocontrast_unsupported_mode():
+    im = Image.new("RGBA", (1, 1))
+    with pytest.raises(OSError):
+        ImageOps.autocontrast(im)
+
+
 def test_autocontrast_cutoff():
     # Test the cutoff argument of autocontrast
     with Image.open("Tests/images/bw_gradient.png") as img:
diff --git a/src/PIL/ImageOps.py b/src/PIL/ImageOps.py
index 6d70f0248..4f83a4edb 100644
--- a/src/PIL/ImageOps.py
+++ b/src/PIL/ImageOps.py
@@ -56,7 +56,7 @@ def _lut(image, lut):
             lut = lut + lut + lut
         return image.point(lut)
     else:
-        msg = "not supported for this image mode"
+        msg = f"not supported for mode {image.mode}"
         raise OSError(msg)