diff --git a/docs/themes.rst b/docs/themes.rst
index 1a206c2..26a3951 100644
--- a/docs/themes.rst
+++ b/docs/themes.rst
@@ -59,6 +59,15 @@ You can use the following variables in your template:
 ``theme.name``, ``theme.url``
     Name and url of the currently used theme.
 
+Filters
+~~~~~~~
+
+You can define custom jinja filters for your template by creating a ``filters.py`` script
+at the root of your template directory.
+
+This script will then be imported and all defined functions will be available as jinja filters
+with the same names in your templates.
+
 Documentation of sigal's main classes
 -------------------------------------
 
diff --git a/sigal/writer.py b/sigal/writer.py
index d2b566f..c8a1df4 100644
--- a/sigal/writer.py
+++ b/sigal/writer.py
@@ -87,8 +87,9 @@ class Writer(object):
         filters_py = os.path.join(self.theme, 'filters.py')
         if os.path.exists(filters_py):
             mod = imp.load_source('filters', filters_py)
-            for name in [name for name in dir(mod) if isinstance(getattr(mod, name), types.FunctionType)]:
-                env.filters[name] = getattr(mod, name)
+            for name in dir(mod):
+                if isinstance(getattr(mod, name), types.FunctionType):
+                    env.filters[name] = getattr(mod, name)
 
         try:
             self.template = env.get_template(self.template_file)