diff --git a/src/calibre/ebooks/pml/pmlml.py b/src/calibre/ebooks/pml/pmlml.py
index f441e20917..1777d1290b 100644
--- a/src/calibre/ebooks/pml/pmlml.py
+++ b/src/calibre/ebooks/pml/pmlml.py
@@ -27,7 +27,7 @@ TAG_MAP = {
     'del'     : 'o',
     'h1'      : 'x',
     'h2'      : 'X0',
-    'h3'      : 'x1',
+    'h3'      : 'X1',
     'h4'      : 'X2',
     'h5'      : 'X3',
     'h6'      : 'X4',