diff --git a/clang/docs/tools/dump_format_style.py b/clang/docs/tools/dump_format_style.py
--- a/clang/docs/tools/dump_format_style.py
+++ b/clang/docs/tools/dump_format_style.py
@@ -225,4 +225,4 @@
 contents = substitute(contents, 'FORMAT_STYLE_OPTIONS', options_text)
 
 with open(DOC_FILE, 'wb') as output:
-  output.write(contents)
+  output.write(contents.encode())