diff --git a/src/PIL/JpegImagePlugin.py b/src/PIL/JpegImagePlugin.py
index c9b83c032..6edaee795 100644
--- a/src/PIL/JpegImagePlugin.py
+++ b/src/PIL/JpegImagePlugin.py
@@ -338,10 +338,11 @@ class JpegImageFile(ImageFile.ImageFile):
 
     def _open(self):
 
-        s = self.fp.read(1)
+        s = self.fp.read(3)
 
-        if i8(s) != 255:
+        if s != b"\xFF\xD8\xFF":
             raise SyntaxError("not a JPEG file")
+        s = b"\xFF"
 
         # Create attributes
         self.bits = self.layers = 0