diff --git a/src/calibre/utils/rapydscript.py b/src/calibre/utils/rapydscript.py
index 2c7a6f53b8..32fa3f2b85 100644
--- a/src/calibre/utils/rapydscript.py
+++ b/src/calibre/utils/rapydscript.py
@@ -272,7 +272,7 @@ def atomic_write(base, name, content):
     name = os.path.join(base, name)
     tname = name + '.tmp'
     with lopen(tname, 'wb') as f:
-        f.write(content)
+        f.write(as_bytes(content))
     atomic_rename(tname, name)