diff --git a/spec/rscons/builders/cfile_spec.rb b/spec/rscons/builders/cfile_spec.rb
index 829f8c9..5605ca4 100644
--- a/spec/rscons/builders/cfile_spec.rb
+++ b/spec/rscons/builders/cfile_spec.rb
@@ -15,6 +15,11 @@ module Rscons
         subject.run("lexer.cc", ["parser.ll"], :cache, env, {})
       end
 
+      it "supports overriding construction variables" do
+        subject.should_receive(:standard_build).with("LEX lexer.c", "lexer.c", ["hi", "parser.l"], ["parser.l"], env, :cache)
+        subject.run("lexer.c", ["parser.l"], :cache, env, "LEX_CMD" => ["hi", "${_SOURCES}"])
+      end
+
       it "raises an error when an unknown source file is specified" do
         expect {subject.run("file.c", ["foo.bar"], :cache, env, {})}.to raise_error /Unknown source file .foo.bar. for CFile builder/
       end
diff --git a/spec/rscons/builders/disassemble_spec.rb b/spec/rscons/builders/disassemble_spec.rb
new file mode 100644
index 0000000..de7c350
--- /dev/null
+++ b/spec/rscons/builders/disassemble_spec.rb
@@ -0,0 +1,17 @@
+module Rscons
+  module Builders
+    describe Disassemble do
+      let(:env) {Environment.new}
+      subject {Disassemble.new}
+
+      it "supports overriding DISASM_CMD construction variable" do
+        cache = "cache"
+        cache.stub(:up_to_date?) { false }
+        cache.stub(:mkdir_p) { }
+        cache.stub(:register_build) { }
+        env.should_receive(:execute).with("Disassemble a_file.txt", ["my_disasm", "a_file.exe"], anything).and_return(true)
+        subject.run("a_file.txt", ["a_file.exe"], cache, env, "DISASM_CMD" => ["my_disasm", "${_SOURCES}"])
+      end
+    end
+  end
+end
diff --git a/spec/rscons/builders/library_spec.rb b/spec/rscons/builders/library_spec.rb
new file mode 100644
index 0000000..8fe4e35
--- /dev/null
+++ b/spec/rscons/builders/library_spec.rb
@@ -0,0 +1,18 @@
+module Rscons
+  module Builders
+    describe Library do
+      let(:env) {Environment.new}
+      subject {Library.new}
+
+      it "supports overriding AR construction variable" do
+        subject.should_receive(:standard_build).with("AR prog.a", "prog.a", ["sp-ar", "rcs", "prog.a", "prog.o"], ["prog.o"], env, :cache)
+        subject.run("prog.a", ["prog.o"], :cache, env, "AR" => "sp-ar")
+      end
+
+      it "supports overriding ARCMD construction variable" do
+        subject.should_receive(:standard_build).with("AR prog.a", "prog.a", ["special", "AR!", "prog.o"], ["prog.o"], env, :cache)
+        subject.run("prog.a", ["prog.o"], :cache, env, "ARCMD" => ["special", "AR!", "${_SOURCES}"])
+      end
+    end
+  end
+end
diff --git a/spec/rscons/builders/object_spec.rb b/spec/rscons/builders/object_spec.rb
new file mode 100644
index 0000000..789d8e3
--- /dev/null
+++ b/spec/rscons/builders/object_spec.rb
@@ -0,0 +1,23 @@
+module Rscons
+  module Builders
+    describe Object do
+      let(:env) {Environment.new}
+      subject {Object.new}
+
+      it "supports overriding CCCMD construction variable" do
+        cache = "cache"
+        cache.stub(:up_to_date?) { false }
+        cache.stub(:mkdir_p) { }
+        cache.stub(:register_build) { }
+        FileUtils.stub(:rm_f) { }
+        File.stub(:exists?) { false }
+        env.should_receive(:execute).with("CC mod.o", ["llc", "mod.c"]).and_return(true)
+        subject.run("mod.o", ["mod.c"], cache, env, "CCCMD" => ["llc", "${_SOURCES}"])
+      end
+
+      it "raises an error when given a source file with an unknown suffix" do
+        expect { subject.run("mod.o", ["mod.xyz"], :cache, env, {}) }.to raise_error /unknown input file type: "mod.xyz"/
+      end
+    end
+  end
+end
diff --git a/spec/rscons/builders/preprocess_spec.rb b/spec/rscons/builders/preprocess_spec.rb
new file mode 100644
index 0000000..2a47213
--- /dev/null
+++ b/spec/rscons/builders/preprocess_spec.rb
@@ -0,0 +1,18 @@
+module Rscons
+  module Builders
+    describe Preprocess do
+      let(:env) {Environment.new}
+      subject {Preprocess.new}
+
+      it "supports overriding CC construction variable" do
+        subject.should_receive(:standard_build).with("Preprocess module.pp", "module.pp", ["my_cpp", "-E", "-o", "module.pp", "module.c"], ["module.c"], env, :cache)
+        subject.run("module.pp", ["module.c"], :cache, env, "CC" => "my_cpp")
+      end
+
+      it "supports overriding CPP_CMD construction variable" do
+        subject.should_receive(:standard_build).with("Preprocess module.pp", "module.pp", ["my_cpp", "module.c"], ["module.c"], env, :cache)
+        subject.run("module.pp", ["module.c"], :cache, env, "CPP_CMD" => ["my_cpp", "${_SOURCES}"])
+      end
+    end
+  end
+end
diff --git a/spec/rscons/builders/program_spec.rb b/spec/rscons/builders/program_spec.rb
new file mode 100644
index 0000000..d81b067
--- /dev/null
+++ b/spec/rscons/builders/program_spec.rb
@@ -0,0 +1,18 @@
+module Rscons
+  module Builders
+    describe Program do
+      let(:env) {Environment.new}
+      subject {Program.new}
+
+      it "supports overriding CC construction variable" do
+        subject.should_receive(:standard_build).with("LD prog", "prog", ["sp-c++", "-o", "prog", "prog.o"], ["prog.o"], env, :cache)
+        subject.run("prog", ["prog.o"], :cache, env, "CC" => "sp-c++")
+      end
+
+      it "supports overriding LDCMD construction variable" do
+        subject.should_receive(:standard_build).with("LD prog", "prog", ["special", "LD!", "prog.o"], ["prog.o"], env, :cache)
+        subject.run("prog", ["prog.o"], :cache, env, "LDCMD" => ["special", "LD!", "${_SOURCES}"])
+      end
+    end
+  end
+end