diff --git a/src/static/js/Changeset.js b/src/static/js/Changeset.js
index cf2b565adee..7419d37519d 100644
--- a/src/static/js/Changeset.js
+++ b/src/static/js/Changeset.js
@@ -924,8 +924,9 @@ exports.textLinesMutator = (lines) => {
           curLine += newLines.length;
           // insert the remaining chars from the "old" line (e.g. the line we were in
           // when we started to insert new lines)
-          curSplice.push(theLine.substring(lineCol));
-          curCol = 0; // TODO(doc) why is this not set to the length of last line?
+          const remaining = theLine.substring(lineCol);
+          if (remaining !== '') curSplice.push(remaining);
+          curCol = 0;
         } else {
           Array.prototype.push.apply(curSplice, newLines);
           curLine += newLines.length;