diff --git a/datasette/publish/heroku.py b/datasette/publish/heroku.py
index 19fe3fbe..2ebbd4bd 100644
--- a/datasette/publish/heroku.py
+++ b/datasette/publish/heroku.py
@@ -175,7 +175,7 @@ def temporary_heroku_directory(
                 fp.write(json.dumps(metadata_content, indent=2))
 
         with open("runtime.txt", "w") as fp:
-            fp.write("python-3.8.7")
+            fp.write("python-3.8.10")
 
         if branch:
             install = [