diff --git a/IPython/html/static/notebook/js/textcell.js b/IPython/html/static/notebook/js/textcell.js
index 377a761..7c519f4 100644
--- a/IPython/html/static/notebook/js/textcell.js
+++ b/IPython/html/static/notebook/js/textcell.js
@@ -515,9 +515,8 @@ var IPython = (function (IPython) {
     HeadingCell.prototype.render = function () {
         if (this.rendered === false) {
             var text = this.get_text();
-            // Markdown headings must be a single line,
-            // truncate invalid input
-            text = text.split('\n')[0];
+            // Markdown headings must be a single line
+            text = text.replace(/\n/g, ' ');
             if (text === "") { text = this.placeholder; }
             text = Array(this.level + 1).join("#") + " " + text;
             text = IPython.mathjaxutils.remove_math(text);