diff --git a/atrcopy/ataridos.py b/atrcopy/ataridos.py
index b78ae03..871f5e8 100644
--- a/atrcopy/ataridos.py
+++ b/atrcopy/ataridos.py
@@ -94,8 +94,8 @@ class AtariDosDirent(Dirent):
         self.deleted = False
         self.num_sectors = 0
         self.starting_sector = 0
-        self.basename = ""
-        self.ext = ""
+        self.basename = b''
+        self.ext = b''
         self.is_sane = True
         self.current_sector = 0
         self.current_read = 0
@@ -103,14 +103,14 @@ class AtariDosDirent(Dirent):
         self.parse_raw_dirent(image, bytes)
 
     def __str__(self):
-        return "File #%-2d (%s) %03d %-8s%-3s  %03d" % (self.file_num, self.summary, self.starting_sector, self.basename, self.ext, self.num_sectors)
+        return "File #%-2d (%s) %03d %-8s%-3s  %03d" % (self.file_num, self.summary, self.starting_sector, str(self.basename), str(self.ext), self.num_sectors)
 
     def __eq__(self, other):
         return self.__class__ == other.__class__ and self.filename == other.filename and self.starting_sector == other.starting_sector and self.num_sectors == other.num_sectors
 
     @property
     def filename(self):
-        ext = ("." + self.ext) if self.ext else ""
+        ext = (b'.' + self.ext) if self.ext else b''
         return self.basename + ext
 
     @property
@@ -138,10 +138,10 @@ class AtariDosDirent(Dirent):
     def extra_metadata(self, image):
         return self.verbose_info
 
-    def parse_raw_dirent(self, image, bytes):
-        if bytes is None:
+    def parse_raw_dirent(self, image, data):
+        if data is None:
             return
-        values = bytes.view(dtype=self.format)[0]
+        values = data.view(dtype=self.format)[0]
         flag = values[0]
         self.flag = flag
         self.opened_output = (flag&0x01) > 0
@@ -153,8 +153,8 @@ class AtariDosDirent(Dirent):
         self.deleted = (flag&0x80) > 0
         self.num_sectors = int(values[1])
         self.starting_sector = int(values[2])
-        self.basename = str(values[3]).rstrip()
-        self.ext = str(values[4]).rstrip()
+        self.basename = bytes(values[3]).rstrip()
+        self.ext = bytes(values[4]).rstrip()
         self.is_sane = self.sanity_check(image)
 
     def encode_dirent(self):
diff --git a/atrcopy/diskimages.py b/atrcopy/diskimages.py
index 3b86dd8..af77572 100644
--- a/atrcopy/diskimages.py
+++ b/atrcopy/diskimages.py
@@ -183,9 +183,9 @@ class DiskImageBase(object):
         if not filename:
             raise RuntimeError("No filename specified for save!")
         if type(filename) is not bytes: filename = filename.encode("utf-8")
-        bytes = self.bytes[:]
+        data = self.bytes[:]
         with open(filename, "wb") as fh:
-            bytes.tofile(fh)
+            data.tofile(fh)
 
     def assert_valid_sector(self, sector):
         if not self.header.sector_is_valid(sector):
@@ -279,7 +279,7 @@ class DiskImageBase(object):
         for dirent in self.files:
             if filename == dirent.filename:
                 return dirent
-        raise FileNotFound("%s not found on disk" % filename)
+        raise FileNotFound("%s not found on disk" % str(filename))
 
     def find_file(self, filename):
         dirent = self.find_dirent(filename)
diff --git a/atrcopy/dos33.py b/atrcopy/dos33.py
index d2efc52..2309769 100644
--- a/atrcopy/dos33.py
+++ b/atrcopy/dos33.py
@@ -171,7 +171,7 @@ class Dos33Dirent(Dirent):
         self.deleted = False
         self.track = 0
         self.sector = 0
-        self.filename = ""
+        self.filename = b''
         self.num_sectors = 0
         self.is_sane = True
         self.current_sector_index = 0
@@ -353,7 +353,8 @@ class Dos33Dirent(Dirent):
         return self.filename
 
     def set_values(self, filename, filetype, index):
-        self.filename = "%-30s" % filename[0:30]
+        if type(filename) is not bytes: filename = filename.encode("utf-8")
+        self.filename = b'%-30s' % filename[0:30]
         self._file_type = self.text_to_type.get(filetype, 0x04)
         self.locked = False
         self.deleted = False
diff --git a/test/test_add_file.py b/test/test_add_file.py
index ffd679f..d755234 100644
--- a/test/test_add_file.py
+++ b/test/test_add_file.py
@@ -18,6 +18,7 @@ class BaseFilesystemModifyTest(object):
         self.image = self.diskimage_type(rawdata)
 
     def check_entries(self, entries, prefix=b"TEST", save=None):
+        if type(prefix) is not bytes: prefix = prefix.encode("utf-8")
         orig_num_files = len(self.image.files)
         filenames = []
         count = 1