diff --git a/lib/minify.js b/lib/minify.js
index d84f6825..a5bcb85d 100644
--- a/lib/minify.js
+++ b/lib/minify.js
@@ -189,7 +189,7 @@ function minify(files, options) {
                 options.output.source_map = SourceMap({
                     file: options.sourceMap.filename,
                     orig: source_maps,
-                    root: options.sourceMap.root
+                    sourceRoot: options.sourceMap.root
                 });
                 if (options.sourceMap.includeSources) {
                     if (files instanceof AST_Toplevel) {