diff --git a/federationapi/internal/perform.go b/federationapi/internal/perform.go
index 970a64653..9100c8f18 100644
--- a/federationapi/internal/perform.go
+++ b/federationapi/internal/perform.go
@@ -213,10 +213,14 @@ func (r *FederationInternalAPI) performJoinUsingServer(
 	// If the remote server returned an event in the "event" key of
 	// the send_join request then we should use that instead. It may
 	// contain signatures that we don't know about.
-	if respSendJoin.Event != nil && isWellFormedMembershipEvent(
-		respSendJoin.Event, roomID, userID, r.cfg.Matrix.ServerName,
-	) {
-		event = respSendJoin.Event
+	if len(respSendJoin.Event) > 0 {
+		var remoteEvent *gomatrixserverlib.Event
+		remoteEvent, err = respSendJoin.Event.UntrustedEvent(respMakeJoin.RoomVersion)
+		if err == nil && isWellFormedMembershipEvent(
+			remoteEvent, roomID, userID, r.cfg.Matrix.ServerName,
+		) {
+			event = remoteEvent
+		}
 	}
 
 	// Sanity-check the join response to ensure that it has a create
diff --git a/federationapi/routing/join.go b/federationapi/routing/join.go
index 9f8d94105..abf9c0945 100644
--- a/federationapi/routing/join.go
+++ b/federationapi/routing/join.go
@@ -403,7 +403,7 @@ func SendJoin(
 			StateEvents: gomatrixserverlib.NewEventJSONsFromHeaderedEvents(stateAndAuthChainResponse.StateEvents),
 			AuthEvents:  gomatrixserverlib.NewEventJSONsFromHeaderedEvents(stateAndAuthChainResponse.AuthChainEvents),
 			Origin:      cfg.Matrix.ServerName,
-			Event:       &signed,
+			Event:       signed.JSON(),
 		},
 	}
 }
diff --git a/go.mod b/go.mod
index 89ff04f63..2513ac87f 100644
--- a/go.mod
+++ b/go.mod
@@ -30,7 +30,7 @@ require (
 	github.com/matrix-org/dugong v0.0.0-20210921133753-66e6b1c67e2e
 	github.com/matrix-org/go-sqlite3-js v0.0.0-20220419092513-28aa791a1c91
 	github.com/matrix-org/gomatrix v0.0.0-20210324163249-be2af5ef2e16
-	github.com/matrix-org/gomatrixserverlib v0.0.0-20220524100759-f98e737f8f9c
+	github.com/matrix-org/gomatrixserverlib v0.0.0-20220525125811-a75fa15a03a0
 	github.com/matrix-org/pinecone v0.0.0-20220408153826-2999ea29ed48
 	github.com/matrix-org/util v0.0.0-20200807132607-55161520e1d4
 	github.com/mattn/go-sqlite3 v1.14.10
diff --git a/go.sum b/go.sum
index 3ffd52182..03e71d4a5 100644
--- a/go.sum
+++ b/go.sum
@@ -795,8 +795,8 @@ github.com/matrix-org/go-sqlite3-js v0.0.0-20220419092513-28aa791a1c91/go.mod h1
 github.com/matrix-org/gomatrix v0.0.0-20190528120928-7df988a63f26/go.mod h1:3fxX6gUjWyI/2Bt7J1OLhpCzOfO/bB3AiX0cJtEKud0=
 github.com/matrix-org/gomatrix v0.0.0-20210324163249-be2af5ef2e16 h1:ZtO5uywdd5dLDCud4r0r55eP4j9FuUNpl60Gmntcop4=
 github.com/matrix-org/gomatrix v0.0.0-20210324163249-be2af5ef2e16/go.mod h1:/gBX06Kw0exX1HrwmoBibFA98yBk/jxKpGVeyQbff+s=
-github.com/matrix-org/gomatrixserverlib v0.0.0-20220524100759-f98e737f8f9c h1:J9krMtVgo4mV/G+mRA1u3GL6nNxdNnuPcs891uIQGic=
-github.com/matrix-org/gomatrixserverlib v0.0.0-20220524100759-f98e737f8f9c/go.mod h1:V5eO8rn/C3rcxig37A/BCeKerLFS+9Avg/77FIeTZ48=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20220525125811-a75fa15a03a0 h1:wmxJJA5dczakTi7UsU/MWuWJY3gmC6RWzTN2S484tHo=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20220525125811-a75fa15a03a0/go.mod h1:V5eO8rn/C3rcxig37A/BCeKerLFS+9Avg/77FIeTZ48=
 github.com/matrix-org/pinecone v0.0.0-20220408153826-2999ea29ed48 h1:W0sjjC6yjskHX4mb0nk3p0fXAlbU5bAFUFeEtlrPASE=
 github.com/matrix-org/pinecone v0.0.0-20220408153826-2999ea29ed48/go.mod h1:ulJzsVOTssIVp1j/m5eI//4VpAGDkMt5NrRuAVX7wpc=
 github.com/matrix-org/util v0.0.0-20190711121626-527ce5ddefc7/go.mod h1:vVQlW/emklohkZnOPwD3LrZUBqdfsbiyO3p1lNV8F6U=