diff --git a/synapse/rest/media/v1/preview_url_resource.py b/synapse/rest/media/v1/preview_url_resource.py
index af11a6b69e..f68e18ea8a 100644
--- a/synapse/rest/media/v1/preview_url_resource.py
+++ b/synapse/rest/media/v1/preview_url_resource.py
@@ -321,7 +321,7 @@ class PreviewUrlResource(DirectServeResource):
                     url,
                     output_stream=f,
                     max_size=self.max_spider_size,
-                    headers={"Accept Language": self.url_preview_accept_language},
+                    headers={"Accept-Language": self.url_preview_accept_language},
                 )
             except SynapseError:
                 # Pass SynapseErrors through directly, so that the servlet
diff --git a/tests/rest/media/v1/test_url_preview.py b/tests/rest/media/v1/test_url_preview.py
index bebc94ecab..2826211f32 100644
--- a/tests/rest/media/v1/test_url_preview.py
+++ b/tests/rest/media/v1/test_url_preview.py
@@ -555,10 +555,10 @@ class URLPreviewTests(unittest.HomeserverTestCase):
         # of the request from Synapse
         self.assertIn(
             (
-                b"Accept language: en-UK\r\n"
-                b"Accept language: en-US;q=0.9\r\n"
-                b"Accept language: fr;q=0.8\r\n"
-                b"Accept language: *;q=0.7"
+                b"Accept-Language: en-UK\r\n"
+                b"Accept-Language: en-US;q=0.9\r\n"
+                b"Accept-Language: fr;q=0.8\r\n"
+                b"Accept-Language: *;q=0.7"
             ),
             server.data,
         )