diff --git a/lib/rscons/builders/object.rb b/lib/rscons/builders/object.rb
index 7650608..798d56b 100644
--- a/lib/rscons/builders/object.rb
+++ b/lib/rscons/builders/object.rb
@@ -79,8 +79,9 @@ module Rscons
       #
       # @param options [Hash] Builder run options.
       #
-      # @return [ThreadedCommand]
-      #   Threaded command to execute.
+      # @return [String, ThreadedCommand]
+      #   Target file name if target is up to date or a {ThreadedCommand}
+      #   to execute to build the target.
       def run(options)
         target, sources, cache, env, vars = options.values_at(:target, :sources, :cache, :env, :vars)
         vars = vars.merge({
@@ -88,14 +89,14 @@ module Rscons
           '_SOURCES' => sources,
           '_DEPFILE' => Rscons.set_suffix(target, env.expand_varref("${DEPFILESUFFIX}", vars)),
         })
-        # Store vars back into options so new keys are accessible in #finalize.
-        options[:vars] = vars
         com_prefix = KNOWN_SUFFIXES.find do |compiler, suffix_var|
           sources.first.end_with?(*env.expand_varref("${#{suffix_var}}"))
         end.tap do |v|
           v.nil? and raise "Error: unknown input file type: #{sources.first.inspect}"
         end.first
         command = env.build_command("${#{com_prefix}CMD}", vars)
+        # Store vars back into options so new keys are accessible in #finalize.
+        options[:vars] = vars
         standard_threaded_build("#{com_prefix} #{target}", target, command, sources, env, cache)
       end
 
@@ -103,7 +104,7 @@ module Rscons
       #
       # @param options [Hash] Builder finalize options.
       #
-      # @return [String,nil]
+      # @return [String, nil]
       #   Name of the target file on success or nil on failure.
       def finalize(options)
         if options[:command_status]
diff --git a/lib/rscons/builders/preprocess.rb b/lib/rscons/builders/preprocess.rb
index 6bc8165..3b9d6f3 100644
--- a/lib/rscons/builders/preprocess.rb
+++ b/lib/rscons/builders/preprocess.rb
@@ -20,15 +20,13 @@ module Rscons
 
       # 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.
-      def run(target, sources, cache, env, vars)
+      # @return [String, ThreadedCommand]
+      #   Target file name if target is up to date or a {ThreadedCommand}
+      #   to execute to build the target.
+      def run(options)
+        target, sources, cache, env, vars = options.values_at(:target, :sources, :cache, :env, :vars)
         if sources.find {|s| s.end_with?(*env.expand_varref("${CXXSUFFIX}", vars))}
           pp_cc = "${CXX}"
           depgen = "${CXXDEPGEN}"
@@ -42,17 +40,27 @@ module Rscons
                           "_SOURCES" => sources,
                           "_DEPFILE" => Rscons.set_suffix(target, env.expand_varref("${DEPFILESUFFIX}", vars)))
         command = env.build_command("${CPP_CMD}", vars)
-        unless cache.up_to_date?(target, command, sources, env)
-          cache.mkdir_p(File.dirname(target))
-          return false unless env.execute("Preprocess #{target}", command)
-          deps = sources
-          if File.exists?(vars["_DEPFILE"])
-            deps += Environment.parse_makefile_deps(vars["_DEPFILE"], nil)
-            FileUtils.rm_f(vars["_DEPFILE"])
+        # Store vars back into options so new keys are accessible in #finalize.
+        options[:vars] = vars
+        standard_threaded_build("#{name} #{target}", target, command, sources, env, cache)
+      end
+
+      # Finalize the build operation.
+      #
+      # @param options [Hash] Builder finalize options.
+      #
+      # @return [String, nil]
+      #   Name of the target file on success or nil on failure.
+      def finalize(options)
+        if options[:command_status]
+          target, deps, cache, env, vars = options.values_at(:target, :sources, :cache, :env, :vars)
+          if File.exists?(vars['_DEPFILE'])
+            deps += Environment.parse_makefile_deps(vars['_DEPFILE'], nil)
+            FileUtils.rm_f(vars['_DEPFILE'])
           end
-          cache.register_build(target, command, deps.uniq, env)
+          cache.register_build(target, options[:tc].command, deps.uniq, env)
+          target
         end
-        target
       end
 
     end
diff --git a/spec/rscons/builders/preprocess_spec.rb b/spec/rscons/builders/preprocess_spec.rb
deleted file mode 100644
index 0f56936..0000000
--- a/spec/rscons/builders/preprocess_spec.rb
+++ /dev/null
@@ -1,48 +0,0 @@
-module Rscons
-  module Builders
-    describe Preprocess do
-
-      let(:env) {Environment.new}
-      subject {Preprocess.new}
-
-      it "supports overriding CC construction variable" do
-        cache = double(Cache)
-        command = %w[my_cpp -E -MMD -MF module.mf -o module.pp module.c]
-        expect(cache).to receive(:up_to_date?).with("module.pp", command, %w[module.c], env).and_return(false)
-        expect(cache).to receive(:mkdir_p).with(".")
-        expect(env).to receive(:execute).with("Preprocess module.pp", command).and_return(true)
-        expect(File).to receive(:exists?).with("module.mf").and_return(true)
-        expect(Environment).to receive(:parse_makefile_deps).with("module.mf", nil).and_return(%w[module.c one.h two.h])
-        expect(FileUtils).to receive(:rm_f).with("module.mf")
-        expect(cache).to receive(:register_build).with("module.pp", command, %w[module.c one.h two.h], env)
-
-        expect(subject.run("module.pp", ["module.c"], cache, env, "CC" => "my_cpp")).to eq("module.pp")
-      end
-
-      it "supports overriding CPP_CMD construction variable" do
-        cache = double(Cache)
-        command = %w[my_cpp module.c]
-        expect(cache).to receive(:up_to_date?).with("module.pp", command, %w[module.c], env).and_return(false)
-        expect(cache).to receive(:mkdir_p).with(".")
-        expect(env).to receive(:execute).with("Preprocess module.pp", command).and_return(true)
-        expect(File).to receive(:exists?).with("module.mf").and_return(true)
-        expect(Environment).to receive(:parse_makefile_deps).with("module.mf", nil).and_return(%w[module.c one.h two.h])
-        expect(FileUtils).to receive(:rm_f).with("module.mf")
-        expect(cache).to receive(:register_build).with("module.pp", command, %w[module.c one.h two.h], env)
-
-        expect(subject.run("module.pp", ["module.c"], cache, env, "CPP_CMD" => ["my_cpp", "${_SOURCES}"])).to eq("module.pp")
-      end
-
-      it "returns false if executing the preprocessor fails" do
-        cache = double(Cache)
-        command = %w[gcc -E -MMD -MF module.mf -o module.pp module.c]
-        expect(cache).to receive(:up_to_date?).with("module.pp", command, %w[module.c], env).and_return(false)
-        expect(cache).to receive(:mkdir_p).with(".")
-        expect(env).to receive(:execute).with("Preprocess module.pp", command).and_return(false)
-
-        expect(subject.run("module.pp", ["module.c"], cache, env, {})).to eq(false)
-      end
-
-    end
-  end
-end