diff --git a/ordigi/filesystem.py b/ordigi/filesystem.py
index 6cfb7fb..7ee100d 100644
--- a/ordigi/filesystem.py
+++ b/ordigi/filesystem.py
@@ -27,13 +27,19 @@ class FileSystem(object):
     """A class for interacting with the file system."""
 
     def __init__(self, cache=False, day_begins=0, dry_run=False, exclude_regex_list=set(),
-            filter_by_ext=(), logger=logging.getLogger(), max_deep=None,
+            filter_by_ext=set(), logger=logging.getLogger(), max_deep=None,
             mode='copy', path_format=None):
         self.cache = cache
         self.day_begins = day_begins
         self.dry_run = dry_run
         self.exclude_regex_list = exclude_regex_list
-        self.filter_by_ext = filter_by_ext
+
+        if '%media' in filter_by_ext:
+            filter_by_ext.remove('%media')
+            self.filter_by_ext = filter_by_ext.union(media.extensions)
+        else:
+            self.filter_by_ext = filter_by_ext
+
         self.items = self.get_items()
         self.logger = logger
         self.max_deep = max_deep
@@ -507,24 +513,13 @@ class FileSystem(object):
 
         return self.summary, has_errors
 
-
-    def get_files_in_path(self, path, extensions=False):
+    def get_files_in_path(self, path, extensions=set()):
         """Recursively get files which match a path and extension.
 
         :param str path string: Path to start recursive file listing
         :param tuple(str) extensions: File extensions to include (whitelist)
         :returns: file_path, subdirs
         """
-        if self.filter_by_ext != () and not extensions:
-            # Filtering  files by extensions.
-            if '%media' in self.filter_by_ext:
-                extensions = set()
-                subclasses = get_all_subclasses()
-                for cls in subclasses:
-                    extensions.update(cls.extensions)
-            else:
-                extensions = self.filter_by_ext
-
         file_list = set()
         if os.path.isfile(path):
             if not self.should_exclude(path, self.exclude_regex_list, True):
@@ -547,7 +542,7 @@ class FileSystem(object):
                 # Then append to the list
                 filename_path = os.path.join(dirname, filename)
                 if (
-                        extensions == False
+                        extensions == set()
                         or os.path.splitext(filename)[1][1:].lower() in extensions
                         and not self.should_exclude(filename_path, compiled_regex_list, False)
                     ):