diff --git a/src/calibre/ebooks/oeb/base.py b/src/calibre/ebooks/oeb/base.py
index 7d22f981bf..25002d8674 100644
--- a/src/calibre/ebooks/oeb/base.py
+++ b/src/calibre/ebooks/oeb/base.py
@@ -77,7 +77,7 @@ def XLINK(name):
 def CALIBRE(name):
     return '{%s}%s' % (CALIBRE_NS, name)
 
-_css_url_re = re.compile(r'url\s*\((.*?)\)', re.I)
+_css_url_re = re.compile(r'url\s*\([\'"]{0,1}(.*?)[\'"]{0,1}\)', re.I)
 _css_import_re = re.compile(r'@import "(.*?)"')
 _archive_re = re.compile(r'[^ ]+')