diff --git a/app/assets/javascripts/openproject.js b/app/assets/javascripts/openproject.js
index 5a37bb348c5e..89bad5580552 100644
--- a/app/assets/javascripts/openproject.js
+++ b/app/assets/javascripts/openproject.js
@@ -115,6 +115,24 @@ window.OpenProject = (function ($) {
       return (str+'').replace(REGEXP_ESCAPE, "\\$1");
     };
 
+    /**
+     * Use select2's escapeMarkup function for correctly escaping
+     * text and preventing XSS.
+     */
+    Helpers.markupEscape = (function(){
+      try {
+        var escapeMarkup = jQuery.fn.select2.defaults.escapeMarkup;
+        if(typeof escapeMarkup === "undefined") {
+          throw 'jQuery.fn.select2.defaults.escapeMarkup is undefined';
+        }
+        return escapeMarkup;
+      } catch (e){
+        console.log('Error: jQuery.fn.select2.defaults.escapeMarkup not found.\n' +
+                    'Exception: ' + e.toString());
+        throw e;
+      }
+    }());
+
     /**
      * replace wrong with right in text
      *
@@ -231,12 +249,13 @@ window.OpenProject = (function ($) {
 
         // fallback to base behavior
         if (result.matches === undefined) {
-          return replaceSpecialChars(format(result.text, query.term));
+          return replaceSpecialChars(
+                  Helpers.markupEscape(format(result.text, query.term)));
         }
 
         // shortcut for empty searches
         if (query.sterm.length === 0) {
-          return result.text;
+          return Helpers.markupEscape(result.text);
         }
 
         var matches = result.matches.slice(),
@@ -248,7 +267,7 @@ window.OpenProject = (function ($) {
           text = Helpers.replace(text, match[0], format(match[0], match[1]));
         }
 
-        return replaceSpecialChars(text);
+        return replaceSpecialChars(Helpers.markupEscape(text));
       };
     })();
 
diff --git a/app/assets/javascripts/timelines_autocompleter.js b/app/assets/javascripts/timelines_autocompleter.js
index a146557a85c2..85df82353e2b 100644
--- a/app/assets/javascripts/timelines_autocompleter.js
+++ b/app/assets/javascripts/timelines_autocompleter.js
@@ -124,18 +124,22 @@
       markup = [];
 
       if (match < 0) {
-        return "<span data-value='" + item.id + "'>" + item.name + "</span>";
+        return "<span data-value='" + item.id + "'>" +
+               OpenProject.Helpers.markupEscape(item.name) + "</span>";
       }
 
-      markup.push(item.name.substring(0, match));
+      markup.push(OpenProject.Helpers.markupEscape(
+                  item.name.substring(0, match)));
       markup.push("<span class='select2-match' data-value='" + item.id + "'>");
-      markup.push(item.name.substring(match, match + tl));
+      markup.push(OpenProject.Helpers.markupEscape(
+                  item.name.substring(match, match + tl)));
       markup.push("</span>");
-      markup.push(item.name.substring(match + tl, item.name.length));
-      return markup.join("")
+      markup.push(OpenProject.Helpers.markupEscape(
+                  item.name.substring(match + tl, item.name.length)));
+      return markup.join("");
     },
     formatSelection: function (item) {
-      return item.name;
+      return OpenProject.Helpers.markupEscape(item.name);
     },
     initSelection: function (element, callback) {
       var data = [];