diff --git a/helper.py b/helper.py
index 55244a0..c9e0fe4 100644
--- a/helper.py
+++ b/helper.py
@@ -404,6 +404,9 @@ def write(self, path, data, m='wb'):
 
     # append to local file
     def append(self, path, data):
+        # Ensure data is in bytes format
+        if isinstance(data, str):
+            data = data.encode('utf-8')
         self.write(path, data, 'ab+')
 
 # ----------------------------------------------------------------------
diff --git a/pjl.py b/pjl.py
index e644d37..4426894 100644
--- a/pjl.py
+++ b/pjl.py
@@ -738,7 +738,7 @@ def do_nvram(self, arg):
             commands = ["@PJL RNVRAM ADDRESS=" + str(n) for n in memspace]
             self.chitchat("Writing copy to " + lpath)
             if os.path.isfile(lpath):
-                file().write(lpath, "")  # empty file
+                file().write(lpath, b"")  # empty file
             for chunk in list(chunks(commands, steps)):
                 str_recv = self.cmd(c.EOL.join(chunk))
                 if not str_recv: