diff --git a/resources/images/sort.png b/resources/images/sort.png
new file mode 100644
index 0000000000..26f911b7a9
Binary files /dev/null and b/resources/images/sort.png differ
diff --git a/src/calibre/ebooks/oeb/polish/css.py b/src/calibre/ebooks/oeb/polish/css.py
index 6911709b77..77c1735119 100644
--- a/src/calibre/ebooks/oeb/polish/css.py
+++ b/src/calibre/ebooks/oeb/polish/css.py
@@ -16,6 +16,7 @@ from calibre import force_unicode
 from calibre.ebooks.oeb.base import OEB_STYLES, OEB_DOCS
 from calibre.ebooks.oeb.normalize_css import normalize_filter_css, normalizers
 from calibre.ebooks.oeb.polish.pretty import pretty_script_or_style
+from calibre.utils.icu import numeric_sort_key
 from css_selectors import Select, SelectorError
 
 
@@ -324,3 +325,37 @@ def remove_property_value(prop, predicate):
             x = x.replace(v.cssText, '').strip()
         prop.propertyValue.cssText = x
     return bool(removed_vals)
+
+
+RULE_PRIORITIES = {t:i for i, t in enumerate((CSSRule.COMMENT, CSSRule.CHARSET_RULE, CSSRule.IMPORT_RULE, CSSRule.NAMESPACE_RULE))}
+
+def sort_sheet(container, sheet_or_text):
+    ''' Sort the rules in a stylesheet. Note that in the general case this can
+    change the effective styles, but for most common sheets, it should be safe.
+    '''
+    sheet = container.parse_css(sheet_or_text) if isinstance(sheet_or_text, unicode) else sheet_or_text
+
+    def text_sort_key(x):
+        return numeric_sort_key(unicode(x or ''))
+
+    def selector_sort_key(x):
+        return (x.specificity, text_sort_key(x.selectorText))
+
+    def rule_sort_key(rule):
+        primary = RULE_PRIORITIES.get(rule.type, len(RULE_PRIORITIES))
+        secondary = text_sort_key(getattr(rule, 'atkeyword', '') or '')
+        tertiary = None
+        if rule.type == CSSRule.STYLE_RULE:
+            primary += 1
+            selectors = sorted(rule.selectorList, key=selector_sort_key)
+            tertiary = selector_sort_key(selectors[0])
+            rule.selectorText = ', '.join(s.selectorText for s in selectors)
+        elif rule.type == CSSRule.FONT_FACE_RULE:
+            try:
+                tertiary = text_sort_key(rule.style.getPropertyValue('font-family'))
+            except Exception:
+                pass
+
+        return primary, secondary, tertiary
+    sheet.cssRules.sort(key=rule_sort_key)
+    return sheet
diff --git a/src/calibre/gui2/tweak_book/__init__.py b/src/calibre/gui2/tweak_book/__init__.py
index f29fb25a72..679ff1db0e 100644
--- a/src/calibre/gui2/tweak_book/__init__.py
+++ b/src/calibre/gui2/tweak_book/__init__.py
@@ -58,7 +58,7 @@ d['global_tools_toolbar'] = [
 ]
 d['global_plugins_toolbar'] = []
 d['editor_common_toolbar'] = [('editor-' + x) if x else None for x in ('undo', 'redo', None, 'cut', 'copy', 'paste', 'smart-comment')]
-d['editor_css_toolbar'] = ['pretty-current', 'insert-image']
+d['editor_css_toolbar'] = ['pretty-current', 'sort-css', 'insert-image']
 d['editor_xml_toolbar'] = ['pretty-current', 'insert-tag']
 d['editor_html_toolbar'] = ['fix-html-current', 'pretty-current', 'insert-image', 'insert-hyperlink', 'insert-tag', 'change-paragraph']
 d['editor_format_toolbar'] = [('format-text-' + x) if x else x for x in (
diff --git a/src/calibre/gui2/tweak_book/editor/text.py b/src/calibre/gui2/tweak_book/editor/text.py
index 83f70f7698..e101858247 100644
--- a/src/calibre/gui2/tweak_book/editor/text.py
+++ b/src/calibre/gui2/tweak_book/editor/text.py
@@ -17,7 +17,7 @@ from PyQt5.Qt import (
     QColorDialog, QTimer, pyqtSignal)
 
 from calibre import prepare_string_for_xml
-from calibre.gui2.tweak_book import tprefs, TOP
+from calibre.gui2.tweak_book import tprefs, TOP, current_container
 from calibre.gui2.tweak_book.completion.popup import CompletionPopup
 from calibre.gui2.tweak_book.editor import (
     SYNTAX_PROPERTY, SPELL_PROPERTY, SPELL_LOCALE_PROPERTY, store_locale, LINK_PROPERTY)
@@ -332,6 +332,14 @@ class TextEdit(PlainTextEdit):
         from calibre.gui2.tweak_book.editor.comments import smart_comment
         smart_comment(self, self.syntax)
 
+    def sort_css(self):
+        from calibre.gui2.dialogs.confirm_delete import confirm
+        if confirm(_('Sorting CSS rules can in rare cases change the effective styles applied to the book.'
+                     ' Are you sure you want to proceed?'), 'edit-book-confirm-sort-css', parent=self, config_set=tprefs):
+            from calibre.ebooks.oeb.polish.css import sort_sheet
+            text = sort_sheet(current_container(), self.toPlainText()).cssText
+            self.setPlainText(text)
+
     def find(self, pat, wrap=False, marked=False, complete=False, save_match=None):
         if marked:
             return self.find_in_marked(pat, wrap=wrap, save_match=save_match)
diff --git a/src/calibre/gui2/tweak_book/editor/widget.py b/src/calibre/gui2/tweak_book/editor/widget.py
index 72a69dceea..5829057084 100644
--- a/src/calibre/gui2/tweak_book/editor/widget.py
+++ b/src/calibre/gui2/tweak_book/editor/widget.py
@@ -80,6 +80,8 @@ def register_text_editor_actions(_reg, palette):
     ac = reg('format-justify-fill.png', _('&Justify'), ('format_text', 'justify_justify'), 'format-text-justify-fill', (), _('Justify'))
     ac.setToolTip(_('<h3>Justify</h3>Align the paragraph to both the left and right margins'))
 
+    ac = reg('sort.png', _('&Sort style rules'), ('sort_css',), 'editor-sort-css', (),
+             _('Sort the style rules'), syntaxes=('css',))
     ac = reg('view-image.png', _('&Insert image'), ('insert_resource', 'image'), 'insert-image', (),
              _('Insert an image into the text'), syntaxes=('html', 'css'))
     ac.setToolTip(_('<h3>Insert image</h3>Insert an image into the text'))