diff --git a/src/calibre/ebooks/oeb/transforms/flatcss.py b/src/calibre/ebooks/oeb/transforms/flatcss.py
index 1d728a9a04..bfc29978a1 100644
--- a/src/calibre/ebooks/oeb/transforms/flatcss.py
+++ b/src/calibre/ebooks/oeb/transforms/flatcss.py
@@ -16,7 +16,7 @@ from css_parser.css import Property
 
 from calibre import guess_type
 from calibre.ebooks import unit_convert
-from calibre.ebooks.oeb.base import (XHTML, XHTML_NS, CSS_MIME, OEB_STYLES,
+from calibre.ebooks.oeb.base import (XHTML, XHTML_NS, CSS_MIME, OEB_STYLES, SVG_NS,
         namespace, barename, XPath, css_text)
 from calibre.ebooks.oeb.stylizer import Stylizer
 from calibre.utils.filenames import ascii_filename, ascii_text
@@ -352,8 +352,7 @@ class CSSFlattener:
                     cssdict[property] = "%0.5fem" % (value / fsize)
 
     def flatten_node(self, node, stylizer, names, styles, pseudo_styles, psize, item_id, recurse=True):
-        if not isinstance(node.tag, string_or_bytes) \
-           or namespace(node.tag) != XHTML_NS:
+        if not isinstance(node.tag, string_or_bytes) or namespace(node.tag) not in (XHTML_NS, SVG_NS):
             return
         tag = barename(node.tag)
         style = stylizer.style(node)