diff --git a/lib/linguist/vendor.yml b/lib/linguist/vendor.yml
index c87e5294..b1936ab1 100644
--- a/lib/linguist/vendor.yml
+++ b/lib/linguist/vendor.yml
@@ -31,6 +31,7 @@
 - (^|/)bootstrap([^.]*)(\.min)\.(js|css)$
 
 # Vendored dependencies
+- thirdparty/
 - vendors?/
 
 # Debian packaging
diff --git a/test/test_blob.rb b/test/test_blob.rb
index a930c555..3af263c7 100644
--- a/test/test_blob.rb
+++ b/test/test_blob.rb
@@ -216,6 +216,9 @@ class TestBlob < Test::Unit::TestCase
     # Rails vendor/
     assert blob("vendor/plugins/will_paginate/lib/will_paginate.rb").vendored?
 
+    # 'thirdparty' directory
+    assert blob("thirdparty/lib/main.c").vendored?
+
     # C deps
     assert blob("deps/http_parser/http_parser.c").vendored?
     assert blob("deps/v8/src/v8.h").vendored?