diff --git a/TOOLS/file2string.py b/TOOLS/file2string.py
index 002ba4ab60..cb121e4884 100755
--- a/TOOLS/file2string.py
+++ b/TOOLS/file2string.py
@@ -8,7 +8,7 @@
 import sys
 
 def main(infile):
-    conv = ['\\' + oct(c)[2:] for c in range(256)]
+    conv = ['\\' + ("%03o" % c) for c in range(256)]
     safe_chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz" \
                  "0123456789!#%&'()*+,-./:;<=>?[]^_{|}~ "
     for c in safe_chars: