diff --git a/spec/unit/crypto/algorithms/megolm.spec.js b/spec/unit/crypto/algorithms/megolm.spec.js
index 7f86f86ff..79257e6d7 100644
--- a/spec/unit/crypto/algorithms/megolm.spec.js
+++ b/spec/unit/crypto/algorithms/megolm.spec.js
@@ -129,12 +129,16 @@ describe("MegolmDecryption", function() {
                 const deviceInfo = {};
                 mockCrypto.getStoredDevice.andReturn(deviceInfo);
 
-                const awaitEnsureSessions = new Promise((res, rej) => {
-                    mockOlmLib.ensureOlmSessionsForDevices.andCall(() => {
+                mockOlmLib.ensureOlmSessionsForDevices.andReturn(
+                    Promise.resolve({'@alice:foo': {'alidevice': {
+                        sessionId: 'alisession',
+                    }}}),
+                );
+
+                const awaitEncryptForDevice = new Promise((res, rej) => {
+                    mockOlmLib.encryptMessageForDevice.andCall(() => {
                         res();
-                        return Promise.resolve({'@alice:foo': {'alidevice': {
-                            sessionId: 'alisession',
-                        }}});
+                        return Promise.resolve();
                     });
                 });
 
@@ -144,7 +148,7 @@ describe("MegolmDecryption", function() {
                 megolmDecryption.shareKeysWithDevice(keyRequest);
 
                 // it's asynchronous, so we have to wait a bit
-                return awaitEnsureSessions;
+                return awaitEncryptForDevice;
             }).then(() => {
                 // check that it called encryptMessageForDevice with
                 // appropriate args.
diff --git a/src/crypto/OlmDevice.js b/src/crypto/OlmDevice.js
index f53ada53b..184810822 100644
--- a/src/crypto/OlmDevice.js
+++ b/src/crypto/OlmDevice.js
@@ -849,9 +849,9 @@ OlmDevice.prototype.decryptGroupMessage = async function(
  * @param {string} senderKey base64-encoded curve25519 key of the sender
  * @param {sring} sessionId session identifier
  *
- * @returns {boolean} true if we have the keys to this session
+ * @returns {Promise<boolean>} true if we have the keys to this session
  */
-OlmDevice.prototype.hasInboundSessionKeys = function(roomId, senderKey, sessionId) {
+OlmDevice.prototype.hasInboundSessionKeys = async function(roomId, senderKey, sessionId) {
     const s = this._sessionStore.getEndToEndInboundGroupSession(
         senderKey, sessionId,
     );
@@ -880,14 +880,16 @@ OlmDevice.prototype.hasInboundSessionKeys = function(roomId, senderKey, sessionI
  * @param {string} senderKey base64-encoded curve25519 key of the sender
  * @param {string} sessionId session identifier
  *
- * @returns {{chain_index: number, key: string,
+ * @returns {Promise<{chain_index: number, key: string,
  *        forwarding_curve25519_key_chain: Array<string>,
  *        sender_claimed_ed25519_key: string
- *    }}
+ *    }>}
  *    details of the session key. The key is a base64-encoded megolm key in
  *    export format.
  */
-OlmDevice.prototype.getInboundGroupSessionKey = function(roomId, senderKey, sessionId) {
+OlmDevice.prototype.getInboundGroupSessionKey = async function(
+    roomId, senderKey, sessionId,
+) {
     function getKey(session, sessionData) {
         const messageIndex = session.first_known_index();
 
diff --git a/src/crypto/algorithms/megolm.js b/src/crypto/algorithms/megolm.js
index 16cc2e3b0..7c9a6a1f4 100644
--- a/src/crypto/algorithms/megolm.js
+++ b/src/crypto/algorithms/megolm.js
@@ -725,7 +725,7 @@ MegolmDecryption.prototype.onRoomKeyEvent = function(event) {
 /**
  * @inheritdoc
  */
-MegolmDecryption.prototype.hasKeysForKeyRequest = async function(keyRequest) {
+MegolmDecryption.prototype.hasKeysForKeyRequest = function(keyRequest) {
     const body = keyRequest.requestBody;
 
     return this._olmDevice.hasInboundSessionKeys(
@@ -766,10 +766,10 @@ MegolmDecryption.prototype.shareKeysWithDevice = function(keyRequest) {
             + userId + ":" + deviceId,
         );
 
-        const payload = this._buildKeyForwardingMessage(
+        return this._buildKeyForwardingMessage(
             body.room_id, body.sender_key, body.session_id,
         );
-
+    }).then((payload) => {
         const encryptedContent = {
             algorithm: olmlib.OLM_ALGORITHM,
             sender_key: this._olmDevice.deviceCurve25519Key,
@@ -797,10 +797,10 @@ MegolmDecryption.prototype.shareKeysWithDevice = function(keyRequest) {
     }).done();
 };
 
-MegolmDecryption.prototype._buildKeyForwardingMessage = function(
+MegolmDecryption.prototype._buildKeyForwardingMessage = async function(
     roomId, senderKey, sessionId,
 ) {
-    const key = this._olmDevice.getInboundGroupSessionKey(
+    const key = await this._olmDevice.getInboundGroupSessionKey(
         roomId, senderKey, sessionId,
     );