diff --git a/js/crypto.js b/js/crypto.js
index d2341eda6..6f94bc1fa 100644
--- a/js/crypto.js
+++ b/js/crypto.js
@@ -359,6 +359,9 @@ window.crypto = (function() {
 
 	var initSessionFromPreKeyWhisperMessage = function(encodedNumber, message) {
 		var preKeyPair = crypto_storage.getAndRemovePreKeyPair(message.preKeyId);
+		if (message.registrationId != storage.getUnencrypted("registrationId))
+			throw new Error("Got a message encrypted for a different registration");
+
 		var session = crypto_storage.getSessionOrIdentityKeyByBaseKey(encodedNumber, toArrayBuffer(message.baseKey));
 		var open_session = crypto_storage.getOpenSession(encodedNumber);
 		if (preKeyPair === undefined) {
diff --git a/js/options.js b/js/options.js
index 9b8106ed9..2a3520c77 100644
--- a/js/options.js
+++ b/js/options.js
@@ -84,6 +84,7 @@ $('#init-go').click(function() {
 				storage.putEncrypted("password", password);
 				storage.putEncrypted('signaling_key', signaling_key);
 				storage.putUnencrypted("number_id", number_id);
+				storage.putUnencrypted("registrationId", registrationId);
 				$('#verify1done').html('done');
 
 				var register_keys_func = function() {