diff --git a/lib/sprockets/path_utils.rb b/lib/sprockets/path_utils.rb
index c4d37ba75..d46f201a5 100644
--- a/lib/sprockets/path_utils.rb
+++ b/lib/sprockets/path_utils.rb
@@ -162,7 +162,7 @@ def set_pipeline(path, mime_exts, pipeline_exts, pipeline)
     def split_subpath(path, subpath)
       return "" if path == subpath
       path = File.join(path, ''.freeze)
-      if subpath.start_with?(path)
+      if subpath&.start_with?(path)
         subpath[path.length..-1]
       else
         nil
diff --git a/test/test_path_utils.rb b/test/test_path_utils.rb
index 669a85a04..59a2490a8 100644
--- a/test/test_path_utils.rb
+++ b/test/test_path_utils.rb
@@ -109,6 +109,8 @@ def test_split_subpath_from_root_path
     subpath = File.expand_path("../fixtures/default/app/application.js", __FILE__)
     assert_equal "app/application.js", split_subpath(path, subpath)
 
+    assert_equal nil, split_subpath(path, nil)
+
     subpath = File.expand_path("../fixtures/default", __FILE__)
     assert_equal "", split_subpath(path, subpath)