diff --git a/tools/dfu.py b/tools/dfu.py
index 6591436e9e..39d68f3b66 100755
--- a/tools/dfu.py
+++ b/tools/dfu.py
@@ -20,7 +20,7 @@ def consume(fmt, data, names):
 
 
 def cstring(string):
-    return string.split("\0", 1)[0]
+    return string.split(b"\0", 1)[0]
 
 
 def compute_crc(data):