diff --git a/src/node/handler/PadMessageHandler.js b/src/node/handler/PadMessageHandler.js
index 7cdefc65c..68686c9ef 100644
--- a/src/node/handler/PadMessageHandler.js
+++ b/src/node/handler/PadMessageHandler.js
@@ -742,7 +742,16 @@ function handleUserChanges(data, cb)
         return callback(new Error("Can't apply USER_CHANGES "+changeset+" with oldLen " + Changeset.oldLen(changeset) + " to document of length " + prevText.length));
       }
 
-      pad.appendRevision(changeset, thisSession.author);
+      try
+      {
+        pad.appendRevision(changeset, thisSession.author);
+      }
+      catch(e)
+      {
+        client.json.send({disconnect:"badChangeset"});
+        stats.meter('failedChangesets').mark();
+        return callback(e)
+      }
 
       var correctionChangeset = _correctMarkersInPad(pad.atext, pad.pool);
       if (correctionChangeset) {
diff --git a/src/static/js/Changeset.js b/src/static/js/Changeset.js
index 355bef4a9..366ad15f9 100644
--- a/src/static/js/Changeset.js
+++ b/src/static/js/Changeset.js
@@ -903,6 +903,8 @@ exports.pack = function (oldLen, newLen, opsStr, bank) {
  * @params str {string} String to which a Changeset should be applied
  */
 exports.applyToText = function (cs, str) {
+  var totalNrOfLines = str.split("\n").length;
+  var removedLines = 0;
   var unpacked = exports.unpack(cs);
   exports.assert(str.length == unpacked.oldLen, "mismatched apply: ", str.length, " / ", unpacked.oldLen);
   var csIter = exports.opIterator(unpacked.ops);
@@ -916,6 +918,7 @@ exports.applyToText = function (cs, str) {
       assem.append(bankIter.take(op.chars));
       break;
     case '-':
+      removedLines += op.lines;
       strIter.skip(op.chars);
       break;
     case '=':
@@ -923,6 +926,7 @@ exports.applyToText = function (cs, str) {
       break;
     }
   }
+  exports.assert(totalNrOfLines >= removedLines,"cannot remove ", removedLines, " lines from text with ", totalNrOfLines, " lines");
   assem.append(strIter.take(strIter.remaining()));
   return assem.toString();
 };