diff --git a/datasette/utils/asgi.py b/datasette/utils/asgi.py
index 7caa3469..911038ab 100644
--- a/datasette/utils/asgi.py
+++ b/datasette/utils/asgi.py
@@ -251,7 +251,7 @@ async def asgi_send_file(
 ):
     headers = {}
     if filename:
-        headers["Content-Disposition"] = 'attachment; filename="{}"'.format(filename)
+        headers["content-disposition"] = 'attachment; filename="{}"'.format(filename)
     first = True
     headers["content-length"] = str((await aiofiles.os.stat(str(filepath))).st_size)
     async with aiofiles.open(str(filepath), mode="rb") as fp:
@@ -402,4 +402,6 @@ class AsgiFileDownload:
         self.content_type = content_type
 
     async def asgi_send(self, send):
-        return await asgi_send_file(send, self.filepath, content_type=self.content_type)
+        return await asgi_send_file(
+            send, self.filepath, filename=self.filename, content_type=self.content_type
+        )
diff --git a/datasette/views/base.py b/datasette/views/base.py
index 399b1a1f..afed31a2 100644
--- a/datasette/views/base.py
+++ b/datasette/views/base.py
@@ -337,7 +337,7 @@ class DataView(BaseView):
             disposition = 'attachment; filename="{}.csv"'.format(
                 kwargs.get("table", database)
             )
-            headers["Content-Disposition"] = disposition
+            headers["content-disposition"] = disposition
 
         return AsgiStream(stream_fn, headers=headers, content_type=content_type)
 
diff --git a/tests/test_csv.py b/tests/test_csv.py
index 42022726..86e402b5 100644
--- a/tests/test_csv.py
+++ b/tests/test_csv.py
@@ -92,7 +92,7 @@ def test_table_csv_download(app_client):
     assert response.status == 200
     assert "text/csv; charset=utf-8" == response.headers["content-type"]
     expected_disposition = 'attachment; filename="simple_primary_key.csv"'
-    assert expected_disposition == response.headers["Content-Disposition"]
+    assert expected_disposition == response.headers["content-disposition"]
 
 
 def test_csv_with_non_ascii_characters(app_client):
diff --git a/tests/test_html.py b/tests/test_html.py
index e3d3c2fc..346f9ee3 100644
--- a/tests/test_html.py
+++ b/tests/test_html.py
@@ -913,6 +913,11 @@ def test_database_download_for_immutable():
         content_length = download_response.headers["content-length"]
         assert content_length.isdigit()
         assert int(content_length) > 100
+        assert "content-disposition" in download_response.headers
+        assert (
+            download_response.headers["content-disposition"]
+            == 'attachment; filename="fixtures.db"'
+        )
 
 
 def test_database_download_disallowed_for_mutable(app_client):