diff --git a/mbed/mbed.py b/mbed/mbed.py
index 5f826c5f..1e8756a0 100755
--- a/mbed/mbed.py
+++ b/mbed/mbed.py
@@ -394,7 +394,7 @@ def fetch_rev(url, rev):
                 inurl = urlopen(url)
                 with open(rev_file, 'wb') as outfd:
                     data = None
-                    while data != '':
+                    while data != b'':
                         # Download and write the data in 1 MB chunks
                         data = inurl.read(1024 * 1024)
                         outfd.write(data)