diff --git a/js/libtextsecure.js b/js/libtextsecure.js
index e4903f2a..78206dc6 100644
--- a/js/libtextsecure.js
+++ b/js/libtextsecure.js
@@ -34879,7 +34879,7 @@ window.axolotl.protocol = function(storage_interface) {
 
     function getPaddedMessageLength(messageLength) {
         var messageLengthWithTerminator = messageLength + 1;
-        var messagePartCount            = Math.trunc(messageLengthWithTerminator / 160);
+        var messagePartCount            = Math.floor(messageLengthWithTerminator / 160);
 
         if (messageLengthWithTerminator % 160 != 0) {
             messagePartCount++;
diff --git a/libtextsecure/libaxolotl.js b/libtextsecure/libaxolotl.js
index 1f74c7bd..5ead4bc0 100644
--- a/libtextsecure/libaxolotl.js
+++ b/libtextsecure/libaxolotl.js
@@ -34781,7 +34781,7 @@ window.axolotl.protocol = function(storage_interface) {
 
     function getPaddedMessageLength(messageLength) {
         var messageLengthWithTerminator = messageLength + 1;
-        var messagePartCount            = Math.trunc(messageLengthWithTerminator / 160);
+        var messagePartCount            = Math.floor(messageLengthWithTerminator / 160);
 
         if (messageLengthWithTerminator % 160 != 0) {
             messagePartCount++;