diff --git a/src/UserSettingsStore.js b/src/UserSettingsStore.js
index e5dba62ee7..f2f99603d6 100644
--- a/src/UserSettingsStore.js
+++ b/src/UserSettingsStore.js
@@ -149,6 +149,22 @@ module.exports = {
         return MatrixClientPeg.get().setAccountData("im.vector.web.settings", settings);
     },
 
+    getLocalSettings: function() {
+        return localStorage.getItem('mx_local_settings');
+    },
+
+    getLocalSetting: function(type, defaultValue = null) {
+        var settings = this.getLocalSettings();
+        return settings.hasOwnProperty(type) ? settings[type] : null;
+    },
+
+    setLocalSetting: function(type, value) {
+        var settings = this.getLocalSettings();
+        settings[type] = value;
+        // FIXME: handle errors
+        localStorage.setItem('mx_local_settings', settings);
+    },
+
     isFeatureEnabled: function(feature: string): boolean {
         // Disable labs for guests.
         if (MatrixClientPeg.get().isGuest()) return false;
diff --git a/src/components/structures/UserSettings.js b/src/components/structures/UserSettings.js
index 4a1332be8c..a262431f2b 100644
--- a/src/components/structures/UserSettings.js
+++ b/src/components/structures/UserSettings.js
@@ -57,6 +57,18 @@ const SETTINGS_LABELS = [
 */
 ];
 
+const CRYPTO_SETTINGS_LABELS = [
+    {
+        id: 'blacklistUnverifiedDevices',
+        label: 'Never send encrypted messages to unverified devices',
+    },
+    // XXX: this is here for documentation; the actual setting is managed via RoomSettings
+    // {
+    //     id: 'blacklistUnverifiedDevicesPerRoom'
+    //     label: 'Never send encrypted messages to unverified devices in this room',
+    // }
+];
+
 // Enumerate the available themes, with a nice human text label.
 // 'id' gives the key name in the im.vector.web.settings account data event
 // 'value' is the value for that key in the event
@@ -146,6 +158,8 @@ module.exports = React.createClass({
             syncedSettings.theme = 'light';
         }
         this._syncedSettings = syncedSettings;
+
+        this._localSettings = UserSettingsStore.getLocalSettings();
     },
 
     componentDidMount: function() {
@@ -471,10 +485,32 @@ module.exports = React.createClass({
                         <li><label>Device key:</label>            <span><code><b>{identityKey}</b></code></span></li>
                     </ul>
                 </div>
+                 { CRYPTO_SETTINGS_LABELS.map( this._renderLocalSetting ) }
             </div>
         );
     },
 
+    _renderLocalSetting: function(setting) {
+        const client = MatrixClientPeg.get();
+        return <div className="mx_UserSettings_toggle" key={ setting.id }>
+            <input id={ setting.id }
+                   type="checkbox"
+                   defaultChecked={ this._localSettings[setting.id] }
+                   onChange={
+                        e => {
+                            UserSettingsStore.setLocalSetting(setting.id, e.target.checked)
+                            if (setting.id === 'blacklistUnverifiedDevices') { // XXX: this is a bit ugly
+                                client.setGlobalBlacklistUnverifiedDevices(e.target.checked);
+                            }
+                        }
+                    }
+            />
+            <label htmlFor={ setting.id }>
+                { setting.label }
+            </label>
+        </div>;
+    },
+
     _renderDevicesPanel: function() {
         var DevicesPanel = sdk.getComponent('settings.DevicesPanel');
         return (
diff --git a/src/components/views/dialogs/UnknownDeviceDialog.js b/src/components/views/dialogs/UnknownDeviceDialog.js
index aad310c855..8e04414b9c 100644
--- a/src/components/views/dialogs/UnknownDeviceDialog.js
+++ b/src/components/views/dialogs/UnknownDeviceDialog.js
@@ -69,5 +69,7 @@ module.exports = React.createClass({
                 </div>
             </div>
         );
+        // XXX: do we want to give the user the option to enable blacklistUnverifiedDevices for this room (or globally) at this point?
+        // It feels like confused users will likely turn it on and then disappear in a cloud of UISIs...
     }
 });
diff --git a/src/components/views/rooms/RoomSettings.js b/src/components/views/rooms/RoomSettings.js
index e14a929ebe..7283201858 100644
--- a/src/components/views/rooms/RoomSettings.js
+++ b/src/components/views/rooms/RoomSettings.js
@@ -228,11 +228,13 @@ module.exports = React.createClass({
         }
 
         // encryption
-        p = this.saveEncryption();
+        p = this.saveEnableEncryption();
         if (!q.isFulfilled(p)) {
             promises.push(p);
         }
 
+        this.saveBlacklistUnverifiedDevicesPerRoom();
+
         console.log("Performing %s operations: %s", promises.length, JSON.stringify(promises));
         return promises;
     },
@@ -252,11 +254,11 @@ module.exports = React.createClass({
         return this.refs.url_preview_settings.saveSettings();
     },
 
-    saveEncryption: function() {
+    saveEnableEncryption: function() {
         if (!this.refs.encrypt) { return q(); }
 
         var encrypt = this.refs.encrypt.checked;
-        if (!encrypt) { return q(); }
+        if (encrypt) { return q(); }
 
         var roomId = this.props.room.roomId;
         return MatrixClientPeg.get().sendStateEvent(
@@ -265,6 +267,29 @@ module.exports = React.createClass({
         );
     },
 
+    saveBlacklistUnverifiedDevicesPerRoom: function() {
+        if (!this.refs.blacklistUnverified) return;
+        if (this._isRoomBlacklistUnverified() !== this.refs.blacklistUnverified.checked) {
+            this._setRoomBlacklistUnverified(this.refs.blacklistUnverified.checked);
+        }
+    },
+
+    _isRoomBlacklistUnverified: function() {
+        var blacklistUnverifiedDevicesPerRoom = UserSettingsStore.getLocalSettings().blacklistUnverifiedDevicesPerRoom;
+        if (blacklistUnverifiedDevicesPerRoom) {
+            return blacklistUnverifiedDevicesPerRoom[this.props.room.roomId];
+        }
+        return false;
+    },
+
+    _setRoomBlacklistUnverified: function(value) {
+        var blacklistUnverifiedDevicesPerRoom = UserSettingsStore.getLocalSettings().blacklistUnverifiedDevicesPerRoom;
+        blacklistUnverifiedDevicesPerRoom[this.props.room.roomId] = value;
+        UserSettingsStore.setLocalSettings('blacklistUnverifiedDevicesPerRoom', blacklistUnverifiedDevicesPerRoom);
+
+        this.props.room.setBlacklistUnverifiedDevices(value);
+    },
+
     _hasDiff: function(strA, strB) {
         // treat undefined as an empty string because other components may blindly
         // call setName("") when there has been no diff made to the name!
@@ -477,6 +502,16 @@ module.exports = React.createClass({
         var cli = MatrixClientPeg.get();
         var roomState = this.props.room.currentState;
         var isEncrypted = cli.isRoomEncrypted(this.props.room.roomId);
+        var isGlobalBlacklistUnverified = UserSettingsStore.getLocalSettings().blacklistUnverifiedDevices;
+        var isRoomBlacklistUnverified = this._isRoomBlacklistUnverified();
+
+        var settings =
+            <label>
+                <input type="checkbox" ref="blacklistUnverified"
+                       checked={ isGlobalBlacklistUnverified || isRoomBlacklistUnverified }
+                       disabled={ isGlobalBlacklistUnverified || !this.refs.encrypt.checked }/>
+                Never send encrypted messages to unverified devices in this room.
+            </label>;
 
         if (!isEncrypted &&
                 roomState.mayClientSendStateEvent("m.room.encryption", cli)) {
@@ -486,6 +521,7 @@ module.exports = React.createClass({
                     <img className="mx_RoomSettings_e2eIcon" src="img/e2e-unencrypted.svg" width="12" height="12" />
                     Enable encryption (warning: cannot be disabled again!)
                 </label>
+                { settings }
             );
         }
         else {
@@ -497,6 +533,7 @@ module.exports = React.createClass({
                 }
                 Encryption is { isEncrypted ? "" : "not " } enabled in this room.
                 </label>
+                { settings }
             );
         }
     },