diff --git a/emails/loader/local_store.py b/emails/loader/local_store.py
index 22a385f..e88d297 100644
--- a/emails/loader/local_store.py
+++ b/emails/loader/local_store.py
@@ -165,47 +165,59 @@ class FileSystemLoader(BaseLoader):
 
 
 class ZipLoader(BaseLoader):
+
+    """
+    Load files from zip file
+    """
+
+    common_filename_charsets = ['ascii', 'cp866', 'cp1251', 'utf-8']
+
+
     def __init__(self, file, encoding='utf-8', base_path=None):
-        self.zipfile = ZipFile(file, 'r')
+
+        if not isinstance(file, ZipFile):
+            file = ZipFile(file, 'r')
+
+        self.zipfile = file
         self.encoding = encoding
         self.base_path = base_path
-        self._filenames = None
+        self._decoded_filenames = None
+        self._original_filenames = None
 
-    def _decode_zip_filename(self, name):
-        for enc in ('cp866', 'cp1251', 'utf-8'):
+    def _decode_filename(self, name):
+        for enc in self.common_filename_charsets:
             try:
                 return to_unicode(name, enc)
             except UnicodeDecodeError:
                 pass
         return name
 
-    def _unpack_zip(self):
-        if self._filenames is None:
-            self._filenames = {}
-            for name in self.zipfile.namelist():
-                decoded_name = self._decode_zip_filename(name)
-                self._filenames[decoded_name] = name
+    def _unpack(self):
+        if self._decoded_filenames is None:
+            self._original_filenames = set(self.zipfile.namelist())
+            self._decoded_filenames = dict([(self._decode_filename(name), name) for name in self._original_filenames])
 
     def get_file(self, name):
 
         if self.base_path:
             name = path.join(self.base_path, name)
 
-        self._unpack_zip()
+        self._unpack()
 
         if isinstance(name, str):
             name = to_unicode(name, 'utf-8')
 
-        original_name = self._filenames.get(name)
+        if name not in self._original_filenames:
+            name = self._decoded_filenames.get(name)
 
-        if original_name is None:
+        if name is None:
             raise FileNotFound(name)
 
-        return self.zipfile.read(original_name), name
+        return self.zipfile.read(name), name
 
     def list_files(self):
-        self._unpack_zip()
-        return sorted(self._filenames)
+        self._unpack()
+        return sorted(self._decoded_filenames)
 
 
 class MsgLoader(BaseLoader):
@@ -259,7 +271,7 @@ class MsgLoader(BaseLoader):
 
     def add_text_part(self, part):
         self._text_parts.append({'data': self.extract_part_text(part),
-                             'content_type': part.get_content_type()})
+                                 'content_type': part.get_content_type()})
 
     def add_attachment_part(self, part):
         counter = 1