diff --git a/lib/ejs.js b/lib/ejs.js
index 104aadad..aa6322e3 100755
--- a/lib/ejs.js
+++ b/lib/ejs.js
@@ -578,6 +578,8 @@ Template.prototype = {
     var escapeFn = opts.escapeFunction;
     /** @type {FunctionConstructor} */
     var ctor;
+    /** @type {string} */
+    var sanitizedFilename = opts.filename ? JSON.stringify(opts.filename) : 'undefined';
 
     if (!this.source) {
       this.generateSource();
@@ -609,8 +611,7 @@ Template.prototype = {
     if (opts.compileDebug) {
       src = 'var __line = 1' + '\n'
         + '  , __lines = ' + JSON.stringify(this.templateText) + '\n'
-        + '  , __filename = ' + (opts.filename ?
-        JSON.stringify(opts.filename) : 'undefined') + ';' + '\n'
+        + '  , __filename = ' + sanitizedFilename + ';' + '\n'
         + 'try {' + '\n'
         + this.source
         + '} catch (e) {' + '\n'
@@ -636,7 +637,7 @@ Template.prototype = {
     }
     if (opts.compileDebug && opts.filename) {
       src = src + '\n'
-        + '//# sourceURL=' + opts.filename + '\n';
+        + '//# sourceURL=' + sanitizedFilename + '\n';
     }
 
     try {