diff --git a/build_tests/build_dir/build.rb b/build_tests/build_dir/build.rb
index 65b14fd..efc08a9 100644
--- a/build_tests/build_dir/build.rb
+++ b/build_tests/build_dir/build.rb
@@ -1,5 +1,5 @@
 Rscons::Environment.new do |env|
   env.append('CPPPATH' => Dir['src/**/*/'])
-  env.build_dir('src', 'build')
+  env.build_dir(%r{^src/([^/]+)/}, 'build_\\1/')
   env.Program('build_dir', Dir['src/**/*.c'])
 end
diff --git a/lib/rscons/environment.rb b/lib/rscons/environment.rb
index 0c5c1f3..b73ef35 100644
--- a/lib/rscons/environment.rb
+++ b/lib/rscons/environment.rb
@@ -78,7 +78,6 @@ module Rscons
     # Source files from src_dir will produce object files under obj_dir.
     def build_dir(src_dir, obj_dir)
       src_dir = src_dir.gsub('\\', '/') if src_dir.is_a?(String)
-      obj_dir = obj_dir.gsub('\\', '/')
       @build_dirs << [src_dir, obj_dir]
     end
 
@@ -92,7 +91,7 @@ module Rscons
         if src_dir.is_a?(Regexp)
           build_fname.sub!(src_dir, obj_dir)
         else
-          build_fname.sub!(/^#{src_dir}\//, "#{obj_dir}/")
+          build_fname.sub!(%r{^#{src_dir}/}, "#{obj_dir}/")
         end
         build_fname.gsub!('\\', '/')
       end
diff --git a/spec/build_tests_spec.rb b/spec/build_tests_spec.rb
index 0b6237c..a713756 100644
--- a/spec/build_tests_spec.rb
+++ b/spec/build_tests_spec.rb
@@ -130,36 +130,34 @@ EOF
   it 'builds object files in a different build directory' do
     lines = test_dir('build_dir')
     `./build_dir`.should == "Hello from two()\n"
-    File.exists?('build/one/one.o').should be_true
-    File.exists?('build/two/two.o').should be_true
+    File.exists?('build_one/one.o').should be_true
+    File.exists?('build_two/two.o').should be_true
   end
 
   it 'cleans built files' do
     lines = test_dir('build_dir')
     `./build_dir`.should == "Hello from two()\n"
-    File.exists?('build/one/one.o').should be_true
-    File.exists?('build/two/two.o').should be_true
+    File.exists?('build_one/one.o').should be_true
+    File.exists?('build_two/two.o').should be_true
     Rscons.clean
-    File.exists?('build/one/one.o').should be_false
-    File.exists?('build/two/two.o').should be_false
-    File.exists?('build/one').should be_false
-    File.exists?('build/two').should be_false
-    File.exists?('build').should be_false
+    File.exists?('build_one/one.o').should be_false
+    File.exists?('build_two/two.o').should be_false
+    File.exists?('build_one').should be_false
+    File.exists?('build_two').should be_false
     File.exists?('src/one/one.c').should be_true
   end
 
   it 'does not clean created directories if other non-rscons-generated files reside there' do
     lines = test_dir('build_dir')
     `./build_dir`.should == "Hello from two()\n"
-    File.exists?('build/one/one.o').should be_true
-    File.exists?('build/two/two.o').should be_true
-    File.open('build/two/tmp', 'w') { |fh| fh.puts "dum" }
+    File.exists?('build_one/one.o').should be_true
+    File.exists?('build_two/two.o').should be_true
+    File.open('build_two/tmp', 'w') { |fh| fh.puts "dum" }
     Rscons.clean
-    File.exists?('build/one/one.o').should be_false
-    File.exists?('build/two/two.o').should be_false
-    File.exists?('build/one').should be_false
-    File.exists?('build/two').should be_true
-    File.exists?('build').should be_true
+    File.exists?('build_one/one.o').should be_false
+    File.exists?('build_two/two.o').should be_false
+    File.exists?('build_one').should be_false
+    File.exists?('build_two').should be_true
     File.exists?('src/one/one.c').should be_true
   end