diff --git a/js/crypto.js b/js/crypto.js
index b88d3ab17..ba08268a1 100644
--- a/js/crypto.js
+++ b/js/crypto.js
@@ -401,6 +401,15 @@ window.textsecure.crypto = function() {
 		session.indexInfo.closed = new Date().getTime();
 	}
 
+	self.closeOpenSessionForDevice = function(encodedNumber) {
+		var session = crypto_storage.getOpenSession(encodedNumber);
+		if (session === undefined)
+			return;
+
+		closeSession(session);
+		crypto_storage.saveSession(encodedNumber, session);
+	}
+
 	var initSessionFromPreKeyWhisperMessage;
 	var decryptWhisperMessage;
 	var handlePreKeyWhisperMessage = function(from, encodedMessage) {
@@ -570,7 +579,8 @@ window.textsecure.crypto = function() {
 
 							var finalMessage = textsecure.protos.decodePushMessageContentProtobuf(getString(plaintext));
 
-							if ((finalMessage.flags & 1) == 1) // END_SESSION
+							if ((finalMessage.flags & textsecure.protos.PushMessageContentProtobuf.Flags.END_SESSION)
+									== textsecure.protos.PushMessageContentProtobuf.Flags.END_SESSION)
 								closeSession(session);
 
 							crypto_storage.saveSession(encodedNumber, session, registrationId);
diff --git a/js/sendmessage.js b/js/sendmessage.js
index f9267dc68..45ece7f48 100644
--- a/js/sendmessage.js
+++ b/js/sendmessage.js
@@ -209,7 +209,20 @@ window.textsecure.messaging = function() {
 	}
 
 	self.closeSession = function(number) {
-		//TODO
+		var devices = textsecure.storage.devices.getDeviceObjectsForNumber(number);
+		for (i in devices)
+			textsecure.crypto.closeOpenSessionForDevice(devices[i].encodedNumber);
+
+		return new Promise(function(resolve, reject) {
+			var proto = new textsecure.protos.PushMessageContentProtobuf();
+			proto.flags = textsecure.protos.PushMessageContentProtobuf.Flags.END_SESSION;
+			sendMessageProto([number], proto, function(res) {
+				if (res.failure.length > 0)
+					reject(res.failure[0].error);
+				else
+					resolve();
+			});
+		});
 	}
 
 	return self;