diff --git a/src/calibre/ebooks/mobi/reader/mobi6.py b/src/calibre/ebooks/mobi/reader/mobi6.py
index bba572f8dd..eef167655e 100644
--- a/src/calibre/ebooks/mobi/reader/mobi6.py
+++ b/src/calibre/ebooks/mobi/reader/mobi6.py
@@ -29,6 +29,10 @@ class TopazError(ValueError):
     pass
 
 
+class KFXError(ValueError):
+    pass
+
+
 class MobiReader(object):
     PAGE_BREAK_PAT = re.compile(
         r'<\s*/{0,1}\s*mbp:pagebreak((?:\s+[^/>]*){0,1})/{0,1}\s*>\s*(?:<\s*/{0,1}\s*mbp:pagebreak\s*/{0,1}\s*>)*',
@@ -71,6 +75,8 @@ class MobiReader(object):
         raw = stream.read()
         if raw.startswith('TPZ'):
             raise TopazError(_('This is an Amazon Topaz book. It cannot be processed.'))
+        if raw.startswith(b'\xeaDRMION\xee'):
+            raise KFXError(_('This is an Amazon KFX book. It cannot be processed.'))
 
         self.header   = raw[0:72]
         self.name     = self.header[:32].replace('\x00', '')
@@ -890,5 +896,3 @@ def test_mbp_regex():
         ans = MobiReader.PAGE_BREAK_PAT.sub(r'\1', raw)
         if ans != m:
             raise Exception('%r != %r for %r'%(ans, m, raw))
-
-