diff --git a/lib/source-map-consumer.js b/lib/source-map-consumer.js
index a7cabc86..b8d962ac 100644
--- a/lib/source-map-consumer.js
+++ b/lib/source-map-consumer.js
@@ -332,12 +332,13 @@ function BasicSourceMapConsumer(aSourceMap, aSourceMapURL) {
   var version = util.getArg(sourceMap, 'version');
   var sources = util.getArg(sourceMap, 'sources');
   // Sass 3.3 leaves out the 'names' array, so we deviate from the spec (which
-  // requires the array) to play nice here.
-  var names = util.getArg(sourceMap, 'names', []);
-  var sourceRoot = util.getArg(sourceMap, 'sourceRoot', null);
-  var sourcesContent = util.getArg(sourceMap, 'sourcesContent', null);
+  // requires the array) to play nice here. Inlined getArg with default for
+  // the optional fields below — see #59 for the pattern.
+  var names = sourceMap.names != null ? sourceMap.names : [];
+  var sourceRoot = sourceMap.sourceRoot != null ? sourceMap.sourceRoot : null;
+  var sourcesContent = sourceMap.sourcesContent != null ? sourceMap.sourcesContent : null;
   var mappings = util.getArg(sourceMap, 'mappings');
-  var file = util.getArg(sourceMap, 'file', null);
+  var file = sourceMap.file != null ? sourceMap.file : null;
 
   // Once again, Sass deviates from the spec and supplies the version as a
   // string rather than a number, so we use loose equality checking here.