diff --git a/roomserver/internal/perform/perform_invite.go b/roomserver/internal/perform/perform_invite.go
index b5ace4f00..b29cb3cde 100644
--- a/roomserver/internal/perform/perform_invite.go
+++ b/roomserver/internal/perform/perform_invite.go
@@ -16,8 +16,8 @@ package perform
 
 import (
 	"context"
+	"errors"
 	"fmt"
-	"strings"
 
 	federationSenderAPI "github.com/matrix-org/dendrite/federationsender/api"
 	"github.com/matrix-org/dendrite/internal/config"
@@ -160,8 +160,10 @@ func (r *Inviter) PerformInvite(
 					Code: api.PerformErrorNotAllowed,
 				}
 
-				if strings.Contains(err.Error(), "value is outside of safe range") {
-					log.Debug("setting error to PerformErrCanonicalJSON")
+				// Ensure we send the correct http code if the json is invalid for
+				// room version 6.
+				if req.RoomVersion == gomatrixserverlib.RoomVersionV6 &&
+					errors.Is(err, gomatrixserverlib.ErrCanonicalJSON) {
 					res.Error.Code = api.PerformErrCanonicalJSON
 				}
 
diff --git a/sytest-whitelist b/sytest-whitelist
index 17bf2581d..354890c63 100644
--- a/sytest-whitelist
+++ b/sytest-whitelist
@@ -496,3 +496,4 @@ Forgetting room does not show up in v2 /sync
 Can forget room you've been kicked from
 Can re-join room if re-invited
 /whois
+Outbound federation rejects invite response which include invalid JSON for room version 6
\ No newline at end of file