diff --git a/bin/lessc b/bin/lessc
index 4907bc36f..8f31be4a8 100755
--- a/bin/lessc
+++ b/bin/lessc
@@ -316,8 +316,8 @@ function printUsage() {
     }
 
     if (sourceMapOptions.sourceMapRootpath === undefined) {
-        var pathToMap = path.dirname(sourceMapFileInline ? output : sourceMapOptions.sourceMapFullFilename),
-            pathToInput = path.dirname(sourceMapOptions.sourceMapInputFilename);
+        var pathToMap = path.dirname(sourceMapFileInline ? output : sourceMapOptions.sourceMapFullFilename || '.'),
+            pathToInput = path.dirname(sourceMapOptions.sourceMapInputFilename || '.');
         sourceMapOptions.sourceMapRootpath = path.relative(pathToMap, pathToInput);
     }