diff --git a/lib/output.js b/lib/output.js
index 396c6a29..40493fcf 100644
--- a/lib/output.js
+++ b/lib/output.js
@@ -303,7 +303,7 @@ function OutputStream(options) {
     var add_mapping = options.source_map ? function(token, name) {
         try {
             if (token) options.source_map.add(
-                token.file || "?",
+                token.file,
                 current_line, current_col,
                 token.line, token.col,
                 (!name && token.type == "name") ? token.value : name
diff --git a/lib/sourcemap.js b/lib/sourcemap.js
index bfffe8f8..f62b43e1 100644
--- a/lib/sourcemap.js
+++ b/lib/sourcemap.js
@@ -69,7 +69,14 @@ function SourceMap(options) {
         orig_maps[consumer.file] = consumer;
     }
     function add(source, gen_line, gen_col, orig_line, orig_col, name) {
-        var originalMap = orig_maps[source] || orig_map;
+        var originalMap;
+        if (source) {
+            originalMap = orig_maps[source] || orig_map;
+        }
+        else {
+            source = "?";
+            originalMap = orig_map;
+        }
 
         if (originalMap) {
             var info = originalMap.originalPositionFor({