diff --git a/lib/generate/template.js b/lib/generate/template.js
index 808217a64..e29464c7a 100644
--- a/lib/generate/template.js
+++ b/lib/generate/template.js
@@ -6,6 +6,10 @@ var parse = require("../parse");
 
 var fs = require('./fs');
 
+swig.setFilter('lines', function(content) {
+    return content.split('\n').length;
+});
+
 // return a templeter for page
 var initTemplate = function(options) {
     var tpl = swig.compileFile(path.resolve(__dirname, '../../templates/page.html'));
diff --git a/templates/includes/book/exercise.html b/templates/includes/book/exercise.html
index 8b1fd1f6f..5d721f983 100644
--- a/templates/includes/book/exercise.html
+++ b/templates/includes/book/exercise.html
@@ -12,7 +12,7 @@
 <div class="message">
     {% autoescape false %}{{ section.content }}{% endautoescape %}
 </div>
-<div class="editor" style="height: {{ section.content.split("\n").length*20 }};">{{ section.code.base }}</div>
+<div class="editor" style="height: {{ section.code.solution|lines*20 }}px">{{ section.code.base }}</div>
 
 <pre class="hidden code-solution">{{ section.code.solution }}</pre>
 <pre class="hidden code-validation">{{ section.code.validation }}</pre>