diff --git a/Tests/images/9bit.j2k b/Tests/images/9bit.j2k
new file mode 100644
index 000000000..174f565fc
Binary files /dev/null and b/Tests/images/9bit.j2k differ
diff --git a/Tests/test_file_jpeg2k.py b/Tests/test_file_jpeg2k.py
index bd114aa11..00eeb0cf9 100644
--- a/Tests/test_file_jpeg2k.py
+++ b/Tests/test_file_jpeg2k.py
@@ -446,3 +446,9 @@ def test_plt_marker() -> None:
         hdr = out.read(2)
         length = _binary.i16be(hdr)
         out.seek(length - 2, os.SEEK_CUR)
+
+def test_9bit():
+    # Test 9-bit images are decoded to I;16
+    with Image.open("Tests/images/9bit.j2k") as im:
+        assert im.mode == "I;16"
+        assert im.size == (128, 128)
diff --git a/src/PIL/Jpeg2KImagePlugin.py b/src/PIL/Jpeg2KImagePlugin.py
index 27f8fbbd0..925a9148c 100644
--- a/src/PIL/Jpeg2KImagePlugin.py
+++ b/src/PIL/Jpeg2KImagePlugin.py
@@ -114,7 +114,7 @@ def _parse_codestream(fp):
 
     size = (xsiz - xosiz, ysiz - yosiz)
     if csiz == 1:
-        if (yrsiz[0] & 0x7F) > 8:
+        if (yrsiz[0] & 0x7F) + 1 > 8:
             mode = "I;16"
         else:
             mode = "L"