diff --git a/test/rubygems/test_gem_ext_cmake_builder.rb b/test/rubygems/test_gem_ext_cmake_builder.rb
index 8c01c12..c896a9e 100644
--- a/test/rubygems/test_gem_ext_cmake_builder.rb
+++ b/test/rubygems/test_gem_ext_cmake_builder.rb
@@ -15,6 +15,13 @@ class TestGemExtCmakeBuilder < Gem::TestCase
 
     FileUtils.mkdir_p @ext
     FileUtils.mkdir_p @dest_path
+
+    @orig_LC_ALL, ENV["LC_ALL"] = ENV["LC_ALL"], "C"
+  end
+
+  def teardown
+    super
+    ENV["LC_ALL"] = @orig_LC_ALL
   end
 
   def test_self_build