diff --git a/src/crypto/index.js b/src/crypto/index.js
index 7c0306e1b..4a6b54075 100644
--- a/src/crypto/index.js
+++ b/src/crypto/index.js
@@ -55,6 +55,7 @@ import {InRoomChannel, InRoomRequests} from "./verification/request/InRoomChanne
 import {ToDeviceChannel, ToDeviceRequests} from "./verification/request/ToDeviceChannel";
 import * as httpApi from "../http-api";
 import {IllegalMethod} from "./verification/IllegalMethod";
+import {KeySignatureUploadError} from "../errors";
 
 const DeviceVerification = DeviceInfo.DeviceVerification;
 
@@ -667,15 +668,34 @@ Crypto.prototype._afterCrossSigningLocalKeyChange = async function() {
     const device = this._deviceList.getStoredDevice(this._userId, this._deviceId);
     const signedDevice = await this._crossSigningInfo.signDevice(this._userId, device);
     logger.info(`Starting background key sig upload for ${this._deviceId}`);
-    this._baseApis.uploadKeySignatures({
-        [this._userId]: {
-            [this._deviceId]: signedDevice,
-        },
-    }).then(() => {
-        logger.info(`Finished background key sig upload for ${this._deviceId}`);
-    }).catch(e => {
-        logger.error(`Error during background key sig upload for ${this._deviceId}`, e);
-    });
+
+    const upload = ({ shouldEmit }) => {
+        return this._baseApis.uploadKeySignatures({
+            [this._userId]: {
+                [this._deviceId]: signedDevice,
+            },
+        }).then((response) => {
+            const { failures } = response || {};
+            if (Object.keys(failures || []).length > 0) {
+                if (shouldEmit) {
+                    this._baseApis.emit(
+                        "crypto.keySignatureUploadFailure",
+                        failures,
+                        "_afterCrossSigningLocalKeyChange",
+                        upload, // continuation
+                    );
+                }
+                throw new KeySignatureUploadError("Key upload failed", { failures });
+            }
+            logger.info(`Finished background key sig upload for ${this._deviceId}`);
+        }).catch(e => {
+            logger.error(
+                `Error during background key sig upload for ${this._deviceId}`,
+                e,
+            );
+        });
+    };
+    upload({ shouldEmit: true });
 
     const shouldUpgradeCb = (
         this._baseApis._cryptoCallbacks.shouldUpgradeDeviceVerifications
@@ -959,12 +979,31 @@ Crypto.prototype.checkOwnCrossSigningTrust = async function() {
 
     const keysToUpload = Object.keys(keySignatures);
     if (keysToUpload.length) {
-        logger.info(`Starting background key sig upload for ${keysToUpload}`);
-        this._baseApis.uploadKeySignatures({ [this._userId]: keySignatures }).then(() => {
-            logger.info(`Finished background key sig upload for ${keysToUpload}`);
-        }).catch(e => {
-            logger.error(`Error during background key sig upload for ${keysToUpload}`, e);
-        });
+        const upload = ({ shouldEmit }) => {
+            logger.info(`Starting background key sig upload for ${keysToUpload}`);
+            return this._baseApis.uploadKeySignatures({ [this._userId]: keySignatures })
+            .then((response) => {
+                const { failures } = response || {};
+                logger.info(`Finished background key sig upload for ${keysToUpload}`);
+                if (Object.keys(failures || []).length > 0) {
+                    if (shouldEmit) {
+                        this._baseApis.emit(
+                            "crypto.keySignatureUploadFailure",
+                            failures,
+                            "checkOwnCrossSigningTrust",
+                            upload,
+                        );
+                    }
+                    throw new KeySignatureUploadError("Key upload failed", { failures });
+                }
+            }).catch(e => {
+                logger.error(
+                    `Error during background key sig upload for ${keysToUpload}`,
+                    e,
+                );
+            });
+        };
+        upload({ shouldEmit: true });
     }
 
     this.emit("userTrustStatusChanged", userId, this.checkUserTrust(userId));
@@ -1605,12 +1644,33 @@ Crypto.prototype.setDeviceVerification = async function(
             );
             const device = await this._crossSigningInfo.signUser(xsk);
             if (device) {
-                logger.info("Uploading signature for " + userId + "...");
-                await this._baseApis.uploadKeySignatures({
-                    [userId]: {
-                        [deviceId]: device,
-                    },
-                });
+                const upload = async ({ shouldEmit }) => {
+                    logger.info("Uploading signature for " + userId + "...");
+                    const response = await this._baseApis.uploadKeySignatures({
+                        [userId]: {
+                            [deviceId]: device,
+                        },
+                    });
+                    const { failures } = response || {};
+                    if (Object.keys(failures || []).length > 0) {
+                        if (shouldEmit) {
+                            this._baseApis.emit(
+                                "crypto.keySignatureUploadFailure",
+                                failures,
+                                "setDeviceVerification",
+                                upload,
+                            );
+                        }
+                        /* Throwing here causes the process to be cancelled and the other
+                        * user to be notified */
+                        throw new KeySignatureUploadError(
+                            "Key upload failed",
+                            { failures },
+                        );
+                    }
+                };
+                await upload({ shouldEmit: true });
+
                 // This will emit events when it comes back down the sync
                 // (we could do local echo to speed things up)
             }
@@ -1659,12 +1719,27 @@ Crypto.prototype.setDeviceVerification = async function(
             userId, DeviceInfo.fromStorage(dev, deviceId),
         );
         if (device) {
-            logger.info("Uploading signature for " + deviceId);
-            await this._baseApis.uploadKeySignatures({
-                [userId]: {
-                    [deviceId]: device,
-                },
-            });
+            const upload = async ({shouldEmit}) => {
+                logger.info("Uploading signature for " + deviceId);
+                const response = await this._baseApis.uploadKeySignatures({
+                    [userId]: {
+                        [deviceId]: device,
+                    },
+                });
+                const { failures } = response || {};
+                if (Object.keys(failures || []).length > 0) {
+                    if (shouldEmit) {
+                        this._baseApis.emit(
+                            "crypto.keySignatureUploadFailure",
+                            failures,
+                            "_afterCrossSigningLocalKeyChange",
+                            upload, // continuation
+                        );
+                    }
+                    throw new KeySignatureUploadError("Key upload failed", { failures });
+                }
+            };
+            await upload({shouldEmit: true});
             // XXX: we'll need to wait for the device list to be updated
         }
     }
diff --git a/src/errors.js b/src/errors.js
index f3d88d643..32d72d9a8 100644
--- a/src/errors.js
+++ b/src/errors.js
@@ -44,3 +44,10 @@ InvalidCryptoStoreError.prototype = Object.create(Error.prototype, {
   },
 });
 Reflect.setPrototypeOf(InvalidCryptoStoreError, Error);
+
+export class KeySignatureUploadError extends Error {
+  constructor(message, value) {
+    super(message);
+    this.value = value;
+  }
+}