diff --git a/.flake8 b/.flake8
index aab9b9b..6c6f545 100644
--- a/.flake8
+++ b/.flake8
@@ -3,3 +3,4 @@
 filename = *.py
 hang-closing = False
 max-line-length = 110
+inline-quotes = double
diff --git a/.travis.yml b/.travis.yml
index 47e0b7c..76ed73b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,7 +3,7 @@ language: python
 python:
   - 3.5
 install:
-  - pip install flake8
+  - pip install flake8 flake8-quotes
 script:
   - ln -s revolt revolt.py
   - flake8 .
diff --git a/revolt/__init__.py b/revolt/__init__.py
index 96ae3bc..39d16cb 100644
--- a/revolt/__init__.py
+++ b/revolt/__init__.py
@@ -7,9 +7,9 @@
 # Distributed under terms of the GPLv3 license.
 
 import gi
-gi.require_versions(dict(WebKit2='4.0',
-                         Gtk='3.0',
-                         GLib='2.0'))
+gi.require_versions(dict(WebKit2="4.0",
+                         Gtk="3.0",
+                         GLib="2.0"))
 
 
 def main(program_path):
diff --git a/revolt/statusicon.py b/revolt/statusicon.py
index fb9d93b..43838fc 100644
--- a/revolt/statusicon.py
+++ b/revolt/statusicon.py
@@ -183,15 +183,15 @@ def __on_popup_menu(self, icon, button, time):
 
     def __on_icon_size_change(self, statusicon, size):
         if size > 31:
-            icon_size = '32'
+            icon_size = "32"
         elif size > 23:
-            icon_size = '24'
+            icon_size = "24"
         else:
-            icon_size = '16'
-        if desktop_is('kde'):  # KDE: see gajim bug #5476
-            icon_size = '32'
-        if desktop_is('mate'):
-            icon_size = '16'
+            icon_size = "16"
+        if desktop_is("kde"):  # KDE: see gajim bug #5476
+            icon_size = "32"
+        if desktop_is("mate"):
+            icon_size = "16"
         self.__load_icons(icon_size)
         self.__draw_icon()
 
diff --git a/revolt/util.py b/revolt/util.py
index b4816b6..62a0a78 100644
--- a/revolt/util.py
+++ b/revolt/util.py
@@ -44,12 +44,12 @@ def cachedproperty(f, doc=None):
 
 def desktop_is(desktopname):
     desktopname = desktopname.lower()
-    if desktopname == 'kde' and os.environ.get('KDE_FULL_SESSION') == 'true':
+    if desktopname == "kde" and os.environ.get("KDE_FULL_SESSION") == "true":
         return True
-    if desktopname == 'mate' and os.environ.get('MATE_DESKTOP_SESSION_ID'):
+    if desktopname == "mate" and os.environ.get("MATE_DESKTOP_SESSION_ID"):
         return True
-    for desktopvarname in ['XDG_SESSION_DESKTOP', 'DESKTOP_SESSION', 'XDG_CURRENT_DESKTOP',
-                           'XDG_SESSION_DESKTOP', 'XDG_MENU_PREFIX', 'GDMSESSION', 'XDG_DATA_DIRS']:
+    for desktopvarname in ["XDG_SESSION_DESKTOP", "DESKTOP_SESSION", "XDG_CURRENT_DESKTOP",
+                           "XDG_SESSION_DESKTOP", "XDG_MENU_PREFIX", "GDMSESSION", "XDG_DATA_DIRS"]:
         desktopvarvalue = os.environ.get(desktopvarname)
         if desktopvarvalue and desktopname in desktopvarvalue.lower():
             return True
diff --git a/revolt/window.py b/revolt/window.py
index 5ad0b5f..c4616ab 100644
--- a/revolt/window.py
+++ b/revolt/window.py
@@ -188,7 +188,7 @@ def __on_show_notification(self, webview, notification):
             notif.set_body(notification.get_body())
             # TODO: Use the avatar of the contact, if available.
             notif.set_icon(self._notification_icon)
-            if not desktop_is('xfce'):  # Workaround for XFCE bug #13586
+            if not desktop_is("xfce"):  # Workaround for XFCE bug #13586
                 notif.set_priority(Gio.NotificationPriority.HIGH)
             # use title as notification id:
             # allows to reuse one notification for the same conversation