diff --git a/changelog.d/8862.bugfix b/changelog.d/8862.bugfix
new file mode 100644
index 000000000..bdbd633f7
--- /dev/null
+++ b/changelog.d/8862.bugfix
@@ -0,0 +1 @@
+Fix a longstanding bug where a 500 error would be returned if the `Content-Length` header was not provided to the upload media resource.
diff --git a/synapse/rest/media/v1/upload_resource.py b/synapse/rest/media/v1/upload_resource.py
index d76f7389e..42febc9af 100644
--- a/synapse/rest/media/v1/upload_resource.py
+++ b/synapse/rest/media/v1/upload_resource.py
@@ -44,7 +44,7 @@ class UploadResource(DirectServeJsonResource):
         requester = await self.auth.get_user_by_req(request)
         # TODO: The checks here are a bit late. The content will have
         # already been uploaded to a tmp file at this point
-        content_length = request.getHeader(b"Content-Length").decode("ascii")
+        content_length = request.getHeader("Content-Length")
         if content_length is None:
             raise SynapseError(msg="Request must specify a Content-Length", code=400)
         if int(content_length) > self.max_upload_size: