diff --git a/federationapi/routing/backfill.go b/federationapi/routing/backfill.go
index 7092c4364..69addcce6 100644
--- a/federationapi/routing/backfill.go
+++ b/federationapi/routing/backfill.go
@@ -73,7 +73,10 @@ func Backfill(
 	}
 	if req.Limit, err = strconv.Atoi(limit); err != nil {
 		util.GetLogger(httpReq.Context()).WithError(err).Error("strconv.Atoi failed")
-		return jsonerror.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.InvalidArgumentValue("limit is invalid format"),
+		}
 	}
 
 	// Query the roomserver.
diff --git a/federationapi/routing/profile.go b/federationapi/routing/profile.go
index 01a70c01b..42fe642ce 100644
--- a/federationapi/routing/profile.go
+++ b/federationapi/routing/profile.go
@@ -46,12 +46,17 @@ func GetProfile(
 	_, domain, err := gomatrixserverlib.SplitID('@', userID)
 	if err != nil {
 		util.GetLogger(httpReq.Context()).WithError(err).Error("gomatrixserverlib.SplitID failed")
-		return jsonerror.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.MissingArgument("Format of user ID is invalid."),
+		}
 	}
 
 	if domain != cfg.Matrix.ServerName {
-		util.GetLogger(httpReq.Context()).WithError(err).Error("domain != cfg.Matrix.ServerName failed")
-		return jsonerror.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.InvalidArgumentValue("Domain does not match this server."),
+		}
 	}
 
 	profile, err := appserviceAPI.RetrieveUserProfile(httpReq.Context(), userID, asAPI, accountDB)