diff --git a/datasette/cli.py b/datasette/cli.py
index 28edd590..ca02afad 100644
--- a/datasette/cli.py
+++ b/datasette/cli.py
@@ -465,7 +465,9 @@ def serve(
         url = "http://{}:{}/".format(host, port)
     if open_browser:
         webbrowser.open(url)
-    uvicorn.run(ds.app(), host=host, port=port, log_level="info", lifespan="on")
+    uvicorn.run(
+        ds.app(), host=host, port=port, log_level="info", lifespan="on", workers=1
+    )
 
 
 async def check_databases(ds):
diff --git a/datasette/publish/heroku.py b/datasette/publish/heroku.py
index 24393b90..0f8564c3 100644
--- a/datasette/publish/heroku.py
+++ b/datasette/publish/heroku.py
@@ -73,10 +73,7 @@ def publish_subcommand(publish):
             "about_url": about_url,
         }
 
-        environment_variables = {
-            # Avoid uvicorn error: https://github.com/simonw/datasette/issues/633
-            "WEB_CONCURRENCY": "1"
-        }
+        environment_variables = {}
         if plugin_secret:
             extra_metadata["plugins"] = {}
             for plugin_name, plugin_setting, setting_value in plugin_secret:
diff --git a/tests/test_publish_heroku.py b/tests/test_publish_heroku.py
index ac2744c1..e0035a83 100644
--- a/tests/test_publish_heroku.py
+++ b/tests/test_publish_heroku.py
@@ -59,15 +59,6 @@ def test_publish_heroku(mock_call, mock_check_output, mock_which):
         assert 0 == result.exit_code, result.output
         mock_call.assert_has_calls(
             [
-                mock.call(
-                    [
-                        "heroku",
-                        "config:set",
-                        "-a",
-                        "f",
-                        "WEB_CONCURRENCY=1",
-                    ]
-                ),
                 mock.call(
                     ["heroku", "builds:create", "-a", "f", "--include-vcs-ignore"]
                 ),