diff --git a/src/PIL/JpegXlImagePlugin.py b/src/PIL/JpegXlImagePlugin.py
index 32ef33f28..425392461 100644
--- a/src/PIL/JpegXlImagePlugin.py
+++ b/src/PIL/JpegXlImagePlugin.py
@@ -25,8 +25,8 @@ except ImportError:
 
 def _accept(prefix: bytes) -> bool:
     is_jxl = (
-        prefix[:2] == b"\xff\x0a"
-        or prefix[:12] == b"\x00\x00\x00\x0c\x4a\x58\x4c\x20\x0d\x0a\x87\x0a"
+        prefix.startswith(b"\xff\x0a")
+        or prefix.startswith(b"\x00\x00\x00\x0c\x4a\x58\x4c\x20\x0d\x0a\x87\x0a")
     )
     if is_jxl and not SUPPORTED:
         msg = "image file could not be identified because JXL support not installed"