diff --git a/renga/notebook.py b/renga/notebook.py
index 7982a2f473..9e15ca188c 100644
--- a/renga/notebook.py
+++ b/renga/notebook.py
@@ -240,7 +240,9 @@ def _save_notebook(self, path, nb):
         file_ = self._resolve_path(path)._obj
 
         with file_.open('w') as fp:
-            fp.write(nbformat.writes(nb, version=nbformat.NO_CONVERT))
+            fp.write(
+                nbformat.writes(nb, version=nbformat.NO_CONVERT).encode(
+                    'utf-8'))
 
     def _resolve_path(self, path):
         """Return a resource based on the specified path."""