diff --git a/js/libtextsecure.js b/js/libtextsecure.js
index ddf023c56..bf44b3413 100644
--- a/js/libtextsecure.js
+++ b/js/libtextsecure.js
@@ -38258,7 +38258,7 @@ axolotlInternal.RecipientRecord = function() {
                 var added = numbers.filter(function(number) { return group.numbers.indexOf(number) < 0; });
 
                 return textsecure.storage.groups.addNumbers(groupId, added).then(function(newGroup) {
-                    if (newGroup.length != numbers.length ||
+                    if (numbers.filter(function(number) { return newGroup.indexOf(number) < 0; }).length != 0 ||
                         newGroup.filter(function(number) { return numbers.indexOf(number) < 0; }).length != 0) {
                         throw new Error("Error calculating group member difference");
                     }
diff --git a/libtextsecure/storage/groups.js b/libtextsecure/storage/groups.js
index 90154a0fd..959966a93 100644
--- a/libtextsecure/storage/groups.js
+++ b/libtextsecure/storage/groups.js
@@ -145,7 +145,7 @@
                 var added = numbers.filter(function(number) { return group.numbers.indexOf(number) < 0; });
 
                 return textsecure.storage.groups.addNumbers(groupId, added).then(function(newGroup) {
-                    if (newGroup.length != numbers.length ||
+                    if (numbers.filter(function(number) { return newGroup.indexOf(number) < 0; }).length != 0 ||
                         newGroup.filter(function(number) { return numbers.indexOf(number) < 0; }).length != 0) {
                         throw new Error("Error calculating group member difference");
                     }