diff --git a/src/calibre/ebooks/oeb/base.py b/src/calibre/ebooks/oeb/base.py
index acab68c091..5959f3a19d 100644
--- a/src/calibre/ebooks/oeb/base.py
+++ b/src/calibre/ebooks/oeb/base.py
@@ -347,13 +347,17 @@ def xml2unicode(root, pretty_print=False):
 def xml2text(elem):
     return etree.tostring(elem, method='text', encoding=unicode, with_tail=False)
 
+def escape_cdata(root):
+    pat = re.compile(r'[<>&]')
+    for elem in root.iterdescendants('{%s}style' % XHTML_NS, '{%s}script' % XHTML_NS):
+        if elem.text and pat.search(elem.text) is not None:
+            elem.text = etree.CDATA(elem.text)
+
 def serialize(data, media_type, pretty_print=False):
     if isinstance(data, etree._Element):
         is_oeb_doc = media_type in OEB_DOCS
         if is_oeb_doc:
-            for style in data.iterfind('.//{http://www.w3.org/1999/xhtml}style'):
-                if style.text and re.search(r'[<>&]', style.text) is not None:
-                    style.text = etree.CDATA(style.text)
+            escape_cdata(data)
         ans = xml2str(data, pretty_print=pretty_print)
         if is_oeb_doc:
             # Convert self closing div|span|a|video|audio|iframe|etc tags