diff --git a/src/calibre/ebooks/conversion/cli.py b/src/calibre/ebooks/conversion/cli.py
index fd99e1e346..a30549cbc3 100644
--- a/src/calibre/ebooks/conversion/cli.py
+++ b/src/calibre/ebooks/conversion/cli.py
@@ -116,6 +116,7 @@ def add_pipeline_options(parser, plumber):
                       'font_size_mapping',
                       'line_height',
                       'linearize_tables',
+                      'extra_css',
                   ]
                   ),
 
diff --git a/src/calibre/ebooks/conversion/plumber.py b/src/calibre/ebooks/conversion/plumber.py
index 2b78aca822..22c11303ad 100644
--- a/src/calibre/ebooks/conversion/plumber.py
+++ b/src/calibre/ebooks/conversion/plumber.py
@@ -219,6 +219,14 @@ OptionRecommendation(name='chapter_mark',
                     'to mark chapters.')
         ),
 
+OptionRecommendation(name='extra_css',
+            recommended_value=None, level=OptionRecommendation.LOW,
+            help=_('Either the path to a CSS stylesheet or raw CSS. '
+                'This CSS will be appended to the style rules from '
+                'the source file, so it can be used to override those '
+                'rules.')
+        ),
+
 
 
 OptionRecommendation(name='read_metadata_from_opf',
@@ -487,6 +495,9 @@ OptionRecommendation(name='language',
         else:
             fkey = map(float, fkey.split(','))
 
+        if self.opts.extra_css and os.path.exists(self.opts.extra_css):
+            self.opts.extra_css = open(self.opts.extra_css, 'rb').read()
+
         flattener = CSSFlattener(fbase=fbase, fkey=fkey,
                 lineh=self.opts.line_height,
                 untable=self.opts.linearize_tables)
diff --git a/src/calibre/ebooks/oeb/stylizer.py b/src/calibre/ebooks/oeb/stylizer.py
index 8bc82883e3..34abea32f5 100644
--- a/src/calibre/ebooks/oeb/stylizer.py
+++ b/src/calibre/ebooks/oeb/stylizer.py
@@ -88,7 +88,7 @@ FONT_SIZE_NAMES = set(['xx-small', 'x-small', 'small', 'medium', 'large',
 class CSSSelector(etree.XPath):
     MIN_SPACE_RE = re.compile(r' *([>~+]) *')
     LOCAL_NAME_RE = re.compile(r"(?<!local-)name[(][)] *= *'[^:]+:")
-    
+
     def __init__(self, css, namespaces=XPNSMAP):
         css = self.MIN_SPACE_RE.sub(r'\1', css)
         path = css_to_xpath(css)
@@ -103,10 +103,10 @@ class CSSSelector(etree.XPath):
             self.css)
 
 
-class Stylizer(object):    
+class Stylizer(object):
     STYLESHEETS = WeakKeyDictionary()
-    
-    def __init__(self, tree, path, oeb, profile=PROFILES['PRS505']):
+
+    def __init__(self, tree, path, oeb, profile=PROFILES['PRS505'], extra_css=''):
         self.oeb = oeb
         self.profile = profile
         self.logger = oeb.logger
@@ -135,6 +135,11 @@ class Stylizer(object):
                         (path, item.href))
                     continue
                 stylesheets.append(sitem.data)
+        if extra_css:
+            text = XHTML_CSS_NAMESPACE + extra_css
+            stylesheet = parser.parseString(text, href=cssname)
+            stylesheet.namespaces['h'] = XHTML_NS
+            stylesheets.append(stylesheet)
         rules = []
         index = 0
         self.stylesheets = set()
@@ -159,7 +164,7 @@ class Stylizer(object):
                 self.style(elem)._update_cssdict(cssdict)
         for elem in xpath(tree, '//h:*[@style]'):
             self.style(elem)._apply_style_attr()
-    
+
     def _fetch_css_file(self, path):
         hrefs = self.oeb.manifest.hrefs
         if path not in hrefs:
@@ -171,7 +176,7 @@ class Stylizer(object):
             return (None, None)
         data = item.data.cssText
         return ('utf-8', data)
-    
+
     def flatten_rule(self, rule, href, index):
         results = []
         if isinstance(rule, CSSStyleRule):
@@ -185,7 +190,7 @@ class Stylizer(object):
             style = self.flatten_style(rule.style)
             self.page_rule.update(style)
         return results
-    
+
     def flatten_style(self, cssstyle):
         style = {}
         for prop in cssstyle:
@@ -202,7 +207,7 @@ class Stylizer(object):
             if size in FONT_SIZE_NAMES:
                 style['font-size'] = "%dpt" % self.profile.fnames[size]
         return style
-    
+
     def _normalize_edge(self, cssvalue, name):
         style = {}
         if isinstance(cssvalue, CSSValueList):
@@ -224,7 +229,7 @@ class Stylizer(object):
         for edge, value in itertools.izip(edges, values):
             style["%s-%s" % (name, edge)] = value
         return style
-        
+
     def _normalize_font(self, cssvalue):
         composition = ('font-style', 'font-variant', 'font-weight',
                        'font-size', 'line-height', 'font-family')
@@ -271,7 +276,7 @@ class Stylizer(object):
 
 class Style(object):
     UNIT_RE = re.compile(r'^(-*[0-9]*[.]?[0-9]*)\s*(%|em|px|mm|cm|in|pt|pc)$')
-    
+
     def __init__(self, element, stylizer):
         self._element = element
         self._profile = stylizer.profile
@@ -285,7 +290,7 @@ class Style(object):
 
     def _update_cssdict(self, cssdict):
         self._style.update(cssdict)
-    
+
     def _apply_style_attr(self):
         attrib = self._element.attrib
         if 'style' not in attrib:
@@ -297,7 +302,7 @@ class Style(object):
         except CSSSyntaxError:
             return
         self._style.update(self._stylizer.flatten_style(style))
-    
+
     def _has_parent(self):
         return (self._element.getparent() is not None)
 
@@ -346,7 +351,7 @@ class Style(object):
             elif unit == 'in':
                 result = value * 72.0
             elif unit == 'pt':
-                result = value 
+                result = value
             elif unit == 'em':
                 font = font or self.fontSize
                 result = value * font
@@ -421,7 +426,7 @@ class Style(object):
                 result = self._unit_convert(width, base=base)
             self._width = result
         return self._width
-    
+
     @property
     def height(self):
         if self._height is None:
@@ -463,27 +468,27 @@ class Style(object):
                 result = 1.2 * self.fontSize
             self._lineHeight = result
         return self._lineHeight
-    
+
     @property
     def marginTop(self):
         return self._unit_convert(
             self._get('margin-top'), base=self.height)
-    
+
     @property
     def marginBottom(self):
         return self._unit_convert(
             self._get('margin-bottom'), base=self.height)
-    
+
     @property
     def paddingTop(self):
         return self._unit_convert(
             self._get('padding-top'), base=self.height)
-    
+
     @property
     def paddingBottom(self):
         return self._unit_convert(
             self._get('padding-bottom'), base=self.height)
-    
+
     def __str__(self):
         items = self._style.items()
         items.sort()
diff --git a/src/calibre/ebooks/oeb/transforms/flatcss.py b/src/calibre/ebooks/oeb/transforms/flatcss.py
index b33042e10b..ca96d28a8d 100644
--- a/src/calibre/ebooks/oeb/transforms/flatcss.py
+++ b/src/calibre/ebooks/oeb/transforms/flatcss.py
@@ -116,7 +116,8 @@ class CSSFlattener(object):
         profile = self.context.source
         for item in self.oeb.spine:
             html = item.data
-            stylizer = Stylizer(html, item.href, self.oeb, profile)
+            stylizer = Stylizer(html, item.href, self.oeb, profile,
+                    extra_css=self.context.extra_css)
             self.stylizers[item] = stylizer
 
     def baseline_node(self, node, stylizer, sizes, csize):