diff --git a/src/github.com/matrix-org/dendrite/clientapi/thirdpartyinvites/thirdpartyinvites.go b/src/github.com/matrix-org/dendrite/clientapi/thirdpartyinvites/thirdpartyinvites.go
index c998a6522..ba55a7cad 100644
--- a/src/github.com/matrix-org/dendrite/clientapi/thirdpartyinvites/thirdpartyinvites.go
+++ b/src/github.com/matrix-org/dendrite/clientapi/thirdpartyinvites/thirdpartyinvites.go
@@ -47,7 +47,7 @@ type MembershipRequest struct {
 	Address  string `json:"address"`
 }
 
-// idServerLookupResponse represents the response described at https://matrix.org/docs/spec/client_server/r0.2.0.html#get-matrix-identity-api-v1-lookup
+// idServerLookupResponse represents the response described at https://matrix.org/docs/spec/identity_service/unstable.html#get-matrix-identity-api-v1-lookup
 type idServerLookupResponse struct {
 	TS         int64                        `json:"ts"`
 	NotBefore  int64                        `json:"not_before"`
@@ -58,7 +58,7 @@ type idServerLookupResponse struct {
 	Signatures map[string]map[string]string `json:"signatures"`
 }
 
-// idServerLookupResponse represents the response described at https://matrix.org/docs/spec/client_server/r0.2.0.html#invitation-storage
+// idServerLookupResponse represents the response described at https://matrix.org/docs/spec/identity_service/unstable.html#invitation-storage
 type idServerStoreInviteResponse struct {
 	PublicKey   string             `json:"public_key"`
 	Token       string             `json:"token"`
diff --git a/src/github.com/matrix-org/dendrite/roomserver/input/events.go b/src/github.com/matrix-org/dendrite/roomserver/input/events.go
index 88c604478..e7015b587 100644
--- a/src/github.com/matrix-org/dendrite/roomserver/input/events.go
+++ b/src/github.com/matrix-org/dendrite/roomserver/input/events.go
@@ -22,6 +22,8 @@ import (
 	"github.com/matrix-org/dendrite/roomserver/state"
 	"github.com/matrix-org/dendrite/roomserver/types"
 	"github.com/matrix-org/gomatrixserverlib"
+
+	"github.com/Sirupsen/logrus"
 )
 
 // A RoomEventDatabase has the storage APIs needed to store a room event.
@@ -56,6 +58,15 @@ func processRoomEvent(db RoomEventDatabase, ow OutputRoomEventWriter, input api.
 	// Parse and validate the event JSON
 	event := input.Event
 
+	if err := checkThirdPartyKeys(input.Event); err != nil {
+		// At least one of the key could not be validated. The specification
+		// says that it should not cause a rejection of the event.
+		// https://matrix.org/docs/spec/client_server/r0.2.0.html#id58
+		// There is no direct way to warn the users that the member's
+		// membership is questionable, so log the error as a warning.
+		logrus.Warn(err)
+	}
+
 	// Check that the event passes authentication checks and work out the numeric IDs for the auth events.
 	authEventNIDs, err := checkAuthEvents(db, event, input.AuthEventIDs)
 	if err != nil {
diff --git a/src/github.com/matrix-org/dendrite/roomserver/input/thirdpartyinvites.go b/src/github.com/matrix-org/dendrite/roomserver/input/thirdpartyinvites.go
new file mode 100644
index 000000000..5023375ce
--- /dev/null
+++ b/src/github.com/matrix-org/dendrite/roomserver/input/thirdpartyinvites.go
@@ -0,0 +1,64 @@
+// Copyright 2017 Vector Creations Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package input
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+
+	"github.com/matrix-org/dendrite/common"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+// checkThirdPartyKeys checks the validity of all the public keys in a given
+// m.room.third_party_invite event.
+// Returns with an error if a key could not be verified.
+func checkThirdPartyKeys(event gomatrixserverlib.Event) error {
+	if event.Type() == "m.room.third_party_invite" {
+		var content common.ThirdPartyInviteContent
+		if err := json.Unmarshal(event.Content(), &content); err != nil {
+			return err
+		}
+
+		for _, key := range content.PublicKeys {
+			url := fmt.Sprintf("%s?public_key=%s", key.KeyValidityURL, key.PublicKey)
+			resp, err := http.Get(url)
+			if err != nil {
+				return err
+			}
+
+			if resp.StatusCode != http.StatusOK {
+				errMsg := fmt.Sprintf("Could not verify the validity of key %s at %s", key.PublicKey, key.KeyValidityURL)
+				return errors.New(errMsg)
+			}
+
+			var validity struct {
+				Valid bool `json:"valid"`
+			}
+			if err := json.NewDecoder(resp.Body).Decode(&validity); err != nil {
+				return err
+			}
+
+			if !validity.Valid {
+				errMsg := fmt.Sprintf("Invalid key %s according to %s", key.PublicKey, key.KeyValidityURL)
+				return errors.New(errMsg)
+			}
+		}
+	}
+
+	return nil
+}