diff --git a/build_tests/simple/command_builder.rb b/build_tests/simple/command_builder.rb
new file mode 100644
index 0000000..5b1c02d
--- /dev/null
+++ b/build_tests/simple/command_builder.rb
@@ -0,0 +1,7 @@
+Rscons::Environment.new do |env|
+  command = %W[gcc -o ${_TARGET} ${_SOURCES}]
+  env.Command("simple.exe",
+              "simple.c",
+              "CMD" => command,
+              "CMD_DESC" => "BuildIt")
+end
diff --git a/lib/rscons/builders/command.rb b/lib/rscons/builders/command.rb
index 797d7ed..5403e37 100644
--- a/lib/rscons/builders/command.rb
+++ b/lib/rscons/builders/command.rb
@@ -9,16 +9,14 @@ module Rscons
     #   env.Command("docs.html", "docs.md",
     #               CMD => %w[pandoc -fmarkdown -thtml -o${_TARGET} ${_SOURCES}])
     class Command < Builder
+
       # Run the builder to produce a build target.
       #
-      # @param target [String] Target file name.
-      # @param sources [Array<String>] Source file name(s).
-      # @param cache [Cache] The Cache object.
-      # @param env [Environment] The Environment executing the builder.
-      # @param vars [Hash,VarSet] Extra construction variables.
+      # @param options [Hash] Builder run options.
       #
-      # @return [String,false]
-      #   Name of the target file on success or false on failure.
+      # @return [String, ThreadedCommand]
+      #   Target file name if target is up to date or a {ThreadedCommand}
+      #   to execute to build the target.
       def run(target, sources, cache, env, vars)
         vars = vars.merge({
           "_TARGET" => target,
@@ -26,8 +24,20 @@ module Rscons
         })
         command = env.build_command("${CMD}", vars)
         cmd_desc = vars["CMD_DESC"] || "Command"
-        standard_build("#{cmd_desc} #{target}", target, command, sources, env, cache)
+        standard_threaded_build("#{cmd_desc} #{target}", target, command, sources, env, cache)
       end
+
+      # Finalize a build.
+      #
+      # @param options [Hash]
+      #   Finalize options.
+      #
+      # @return [String, nil]
+      #   The target name on success or nil on failure.
+      def finalize(options)
+        standard_finalize(options)
+      end
+
     end
   end
 end
diff --git a/spec/build_tests_spec.rb b/spec/build_tests_spec.rb
index af71f26..2e7ff1e 100644
--- a/spec/build_tests_spec.rb
+++ b/spec/build_tests_spec.rb
@@ -706,6 +706,21 @@ EOF
     end
   end
 
+  context "Command builder" do
+    it "allows executing an arbitrary command" do
+      test_dir('simple')
+
+      result = run_test(rsconsfile: "command_builder.rb")
+      expect(result.stderr).to eq ""
+      expect(lines(result.stdout)).to eq ["BuildIt simple.exe"]
+      expect(`./simple.exe`).to eq "This is a simple C program\n"
+
+      result = run_test(rsconsfile: "command_builder.rb")
+      expect(result.stderr).to eq ""
+      expect(result.stdout).to eq ""
+    end
+  end
+
   context "Directory builder" do
     it "creates the requested directory" do
       test_dir("simple")
diff --git a/spec/rscons/builders/command_spec.rb b/spec/rscons/builders/command_spec.rb
deleted file mode 100755
index 96ae96c..0000000
--- a/spec/rscons/builders/command_spec.rb
+++ /dev/null
@@ -1,18 +0,0 @@
-module Rscons
-  module Builders
-    describe Command do
-
-      let(:command) { ['pandoc', '-fmarkdown', '-thtml', '-o${_TARGET}', '${_SOURCES}'] }
-      let(:env) {Environment.new}
-      subject {Command.new}
-
-      it "invokes the command to build the target" do
-        expected_cmd = ['pandoc', '-fmarkdown', '-thtml', '-ofoo.html', 'foo.md']
-        expect(subject).to receive(:standard_build).with("PANDOC foo.html", "foo.html", expected_cmd, ["foo.md"], env, :cache)
-        subject.run("foo.html", ["foo.md"], :cache, env,
-                    "CMD" => command, "CMD_DESC" => "PANDOC")
-      end
-
-    end
-  end
-end