diff --git a/lib/builder.js b/lib/builder.js
index b0ca0eb..d12be33 100644
--- a/lib/builder.js
+++ b/lib/builder.js
@@ -105,7 +105,7 @@ function minify(output, fileName, mangle) {
 }
 
 function writeOutputFile(opts, output, basePath) {
-  if (opts.sourceMaps) {
+  if (output.sourceMaps) {
     var sourceMapFile = path.basename(opts.outFile) + '.map';
     output.source += '\n//# sourceMappingURL=' + sourceMapFile;
   }