diff --git a/spec/unit/crypto/algorithms/megolm.spec.js b/spec/unit/crypto/algorithms/megolm.spec.js
index e629385a0..c2646c726 100644
--- a/spec/unit/crypto/algorithms/megolm.spec.js
+++ b/spec/unit/crypto/algorithms/megolm.spec.js
@@ -598,6 +598,7 @@ describe("MegolmDecryption", function() {
             aliceClient.initCrypto(),
             bobClient.initCrypto(),
         ]);
+        aliceClient._crypto.downloadKeys = async () => {};
         const bobDevice = bobClient._crypto._olmDevice;
 
         const roomId = "!someroom";
@@ -649,6 +650,7 @@ describe("MegolmDecryption", function() {
             bobClient.initCrypto(),
         ]);
         const bobDevice = bobClient._crypto._olmDevice;
+        aliceClient._crypto.downloadKeys = async () => {};
 
         const roomId = "!someroom";
 
diff --git a/src/crypto/algorithms/megolm.js b/src/crypto/algorithms/megolm.js
index 8c9ef81f0..b74a856a3 100644
--- a/src/crypto/algorithms/megolm.js
+++ b/src/crypto/algorithms/megolm.js
@@ -1260,17 +1260,25 @@ MegolmDecryption.prototype.onRoomKeyWithheldEvent = async function(event) {
             this.retryDecryptionFromSender(senderKey);
             return;
         }
-        const device = this._crypto._deviceList.getDeviceByIdentityKey(
+        let device = this._crypto._deviceList.getDeviceByIdentityKey(
             content.algorithm, senderKey,
         );
         if (!device) {
-            logger.info(
-                "Couldn't find device for identity key " + senderKey +
-                    ": not establishing session",
+            // if we don't know about the device, fetch the user's devices again
+            // and retry before giving up
+            await this._crypto.downloadKeys([sender], false);
+            device = this._crypto._deviceList.getDeviceByIdentityKey(
+                content.algorithm, senderKey,
             );
-            await this._olmDevice.recordSessionProblem(senderKey, "no_olm", false);
-            this.retryDecryptionFromSender(senderKey);
-            return;
+            if (!device) {
+                logger.info(
+                    "Couldn't find device for identity key " + senderKey +
+                        ": not establishing session",
+                );
+                await this._olmDevice.recordSessionProblem(senderKey, "no_olm", false);
+                this.retryDecryptionFromSender(senderKey);
+                return;
+            }
         }
         await olmlib.ensureOlmSessionsForDevices(
             this._olmDevice, this._baseApis, {[sender]: [device]}, false,
diff --git a/src/crypto/index.js b/src/crypto/index.js
index 90adf8a01..b59cdf895 100644
--- a/src/crypto/index.js
+++ b/src/crypto/index.js
@@ -2723,15 +2723,21 @@ Crypto.prototype._onToDeviceBadEncrypted = async function(event) {
     // on a current session.
     // Note that an undecryptable message from another device could easily be spoofed -
     // is there anything we can do to mitigate this?
-    const device = this._deviceList.getDeviceByIdentityKey(algorithm, deviceKey);
+    let device = this._deviceList.getDeviceByIdentityKey(algorithm, deviceKey);
     if (!device) {
-        logger.info(
-            "Couldn't find device for identity key " + deviceKey +
-            ": not re-establishing session",
-        );
-        await this._olmDevice.recordSessionProblem(deviceKey, "wedged", false);
-        retryDecryption();
-        return;
+        // if we don't know about the device, fetch the user's devices again
+        // and retry before giving up
+        await this.downloadKeys([sender], false);
+        device = this._deviceList.getDeviceByIdentityKey(algorithm, deviceKey);
+        if (!device) {
+            logger.info(
+                "Couldn't find device for identity key " + deviceKey +
+                    ": not re-establishing session",
+            );
+            await this._olmDevice.recordSessionProblem(deviceKey, "wedged", false);
+            retryDecryption();
+            return;
+        }
     }
     const devicesByUser = {};
     devicesByUser[sender] = [device];