diff --git a/spec/build_tests_spec.rb b/spec/build_tests_spec.rb
index c4b176a..bfcab5f 100644
--- a/spec/build_tests_spec.rb
+++ b/spec/build_tests_spec.rb
@@ -37,16 +37,15 @@ describe Rscons do
   end
 
   before(:each) do
-    @output = ""
-    $stdout.stub(:write) do |content|
-      @output += content
-    end
-    $stderr.stub(:write) do |content|
-      @output += content
-    end
+    @saved_stdout = $stdout
+    $stdout = StringIO.new
+    @saved_stderr = $stderr
+    $stderr = StringIO.new
   end
 
   after(:each) do
+    $stdout = @saved_stdout
+    $stderr = @saved_stderr
     Dir.chdir(@owd)
     rm_rf(BUILD_TEST_RUN_DIR)
   end
@@ -68,9 +67,10 @@ describe Rscons do
   end
 
   def lines
-    @output.lines.map(&:rstrip).tap do |v|
-      @output = ""
-    end
+    rv = ($stdout.string + $stderr.string).lines.map(&:rstrip)
+    $stdout.string = ""
+    $stderr.string = ""
+    rv
   end
 
   ###########################################################################
diff --git a/spec/rscons/builders/disassemble_spec.rb b/spec/rscons/builders/disassemble_spec.rb
index a4f759e..d807741 100644
--- a/spec/rscons/builders/disassemble_spec.rb
+++ b/spec/rscons/builders/disassemble_spec.rb
@@ -6,9 +6,9 @@ module Rscons
 
       it "supports overriding DISASM_CMD construction variable" do
         cache = "cache"
-        cache.stub(:up_to_date?) { false }
-        cache.stub(:mkdir_p) { }
-        cache.stub(:register_build) { }
+        allow(cache).to receive(:up_to_date?) { false }
+        allow(cache).to receive(:mkdir_p) { }
+        allow(cache).to receive(:register_build) { }
         expect(env).to 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
diff --git a/spec/rscons/builders/object_spec.rb b/spec/rscons/builders/object_spec.rb
index e5eaded..7c1861c 100644
--- a/spec/rscons/builders/object_spec.rb
+++ b/spec/rscons/builders/object_spec.rb
@@ -6,11 +6,11 @@ module Rscons
 
       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 }
+        allow(cache).to receive(:up_to_date?) { false }
+        allow(cache).to receive(:mkdir_p) { }
+        allow(cache).to receive(:register_build) { }
+        allow(FileUtils).to receive(:rm_f) { }
+        allow(File).to receive(:exists?) { false }
         expect(env).to receive(:execute).with("CC mod.o", ["llc", "mod.c"]).and_return(true)
         subject.run("mod.o", ["mod.c"], cache, env, "CCCMD" => ["llc", "${_SOURCES}"])
       end
diff --git a/spec/rscons/cache_spec.rb b/spec/rscons/cache_spec.rb
index 802425e..4f5d915 100644
--- a/spec/rscons/cache_spec.rb
+++ b/spec/rscons/cache_spec.rb
@@ -1,11 +1,11 @@
 module Rscons
   describe Cache do
     before do
-      File.stub(:read) { nil }
+      allow(File).to receive(:read) { nil }
     end
 
     def build_from(cache)
-      JSON.stub(:load) do
+      allow(JSON).to receive(:load) do
         cache
       end
       Cache.instance.tap do |cache|
@@ -28,7 +28,7 @@ module Rscons
     describe "#clear" do
       it "removes the cache file" do
         expect(FileUtils).to receive(:rm_f).with(Cache::CACHE_FILE)
-        JSON.stub(:load) {{}}
+        allow(JSON).to receive(:load) {{}}
         Cache.instance.clear
       end
     end
@@ -47,7 +47,7 @@ module Rscons
     describe "#up_to_date?" do
       empty_env = "env"
       before do
-        empty_env.stub(:get_user_deps) { nil }
+        allow(empty_env).to receive(:get_user_deps) { nil }
       end
 
       it "returns false when target file does not exist" do
diff --git a/spec/rscons/environment_spec.rb b/spec/rscons/environment_spec.rb
index 185c795..d85b4be 100644
--- a/spec/rscons/environment_spec.rb
+++ b/spec/rscons/environment_spec.rb
@@ -205,7 +205,7 @@ module Rscons
         cache = "cache"
         expect(Cache).to receive(:instance).and_return(cache)
         expect(cache).to receive(:clear_checksum_cache!)
-        env.stub(:run_builder) do |builder, target, sources, cache, vars|
+        allow(env).to receive(:run_builder) do |builder, target, sources, cache, vars|
           raise "Ruby exception thrown by builder"
         end
         expect(cache).to receive(:write)
@@ -349,11 +349,11 @@ module Rscons
             build_op[:vars]["CFLAGS"] += ["-O3", "-DSPECIAL"]
           end
         end
-        env.builders["Object"].stub(:run) do |target, sources, cache, env, vars|
+        allow(env.builders["Object"]).to receive(:run) do |target, sources, cache, env, vars|
           expect(vars["CFLAGS"]).to eq []
         end
         env.run_builder(env.builders["Object"], "build/normal/module.o", ["src/normal/module.c"], "cache", {})
-        env.builders["Object"].stub(:run) do |target, sources, cache, env, vars|
+        allow(env.builders["Object"]).to receive(:run) do |target, sources, cache, env, vars|
           expect(vars["CFLAGS"]).to eq ["-O3", "-DSPECIAL"]
         end
         env.run_builder(env.builders["Object"], "build/special/module.o", ["src/special/module.c"], "cache", {})
diff --git a/spec/rscons_spec.rb b/spec/rscons_spec.rb
index 37e288a..5800fe4 100644
--- a/spec/rscons_spec.rb
+++ b/spec/rscons_spec.rb
@@ -2,23 +2,23 @@ describe Rscons do
   describe ".clean" do
     it "removes all build targets and created directories" do
       cache = "cache"
-      Rscons::Cache.should_receive(:instance).and_return(cache)
-      cache.should_receive(:targets).and_return(["build/a.out", "build/main.o"])
-      FileUtils.should_receive(:rm_f).with("build/a.out")
-      FileUtils.should_receive(:rm_f).with("build/main.o")
-      cache.should_receive(:directories).and_return(["build/one", "build/one/two", "build", "other"])
-      File.should_receive(:directory?).with("build/one/two").and_return(true)
-      Dir.should_receive(:entries).with("build/one/two").and_return([".", ".."])
-      Dir.should_receive(:rmdir).with("build/one/two")
-      File.should_receive(:directory?).with("build/one").and_return(true)
-      Dir.should_receive(:entries).with("build/one").and_return([".", ".."])
-      Dir.should_receive(:rmdir).with("build/one")
-      File.should_receive(:directory?).with("build").and_return(true)
-      Dir.should_receive(:entries).with("build").and_return([".", ".."])
-      Dir.should_receive(:rmdir).with("build")
-      File.should_receive(:directory?).with("other").and_return(true)
-      Dir.should_receive(:entries).with("other").and_return([".", "..", "other.file"])
-      cache.should_receive(:clear)
+      expect(Rscons::Cache).to receive(:instance).and_return(cache)
+      expect(cache).to receive(:targets).and_return(["build/a.out", "build/main.o"])
+      expect(FileUtils).to receive(:rm_f).with("build/a.out")
+      expect(FileUtils).to receive(:rm_f).with("build/main.o")
+      expect(cache).to receive(:directories).and_return(["build/one", "build/one/two", "build", "other"])
+      expect(File).to receive(:directory?).with("build/one/two").and_return(true)
+      expect(Dir).to receive(:entries).with("build/one/two").and_return([".", ".."])
+      expect(Dir).to receive(:rmdir).with("build/one/two")
+      expect(File).to receive(:directory?).with("build/one").and_return(true)
+      expect(Dir).to receive(:entries).with("build/one").and_return([".", ".."])
+      expect(Dir).to receive(:rmdir).with("build/one")
+      expect(File).to receive(:directory?).with("build").and_return(true)
+      expect(Dir).to receive(:entries).with("build").and_return([".", ".."])
+      expect(Dir).to receive(:rmdir).with("build")
+      expect(File).to receive(:directory?).with("other").and_return(true)
+      expect(Dir).to receive(:entries).with("other").and_return([".", "..", "other.file"])
+      expect(cache).to receive(:clear)
 
       Rscons.clean
     end
@@ -35,34 +35,34 @@ describe Rscons do
 
     it "uses the SHELL environment variable if it tests successfully" do
       my_ENV = {"SHELL" => "my_shell"}
-      ENV.stub(:[]) {|*args| my_ENV[*args]}
+      allow(ENV).to receive(:[]) {|*args| my_ENV[*args]}
       io = StringIO.new("success\n")
-      IO.should_receive(:popen).with(["my_shell", "-c", "echo success"]).and_yield(io)
+      expect(IO).to receive(:popen).with(["my_shell", "-c", "echo success"]).and_yield(io)
       expect(Rscons.get_system_shell).to eq(["my_shell", "-c"])
     end
 
     it "uses sh -c on a mingw platform if it tests successfully" do
       my_ENV = {"SHELL" => nil}
-      ENV.stub(:[]) {|*args| my_ENV[*args]}
+      allow(ENV).to receive(:[]) {|*args| my_ENV[*args]}
       io = StringIO.new("success\n")
-      IO.should_receive(:popen).with(["sh", "-c", "echo success"]).and_yield(io)
-      Object.should_receive(:const_get).with("RUBY_PLATFORM").and_return("x86-mingw")
+      expect(IO).to receive(:popen).with(["sh", "-c", "echo success"]).and_yield(io)
+      expect(Object).to receive(:const_get).with("RUBY_PLATFORM").and_return("x86-mingw")
       expect(Rscons.get_system_shell).to eq(["sh", "-c"])
     end
 
     it "uses cmd /c on a mingw platform if sh -c does not test successfully" do
       my_ENV = {"SHELL" => nil}
-      ENV.stub(:[]) {|*args| my_ENV[*args]}
+      allow(ENV).to receive(:[]) {|*args| my_ENV[*args]}
       io = StringIO.new("success\n")
-      IO.should_receive(:popen).with(["sh", "-c", "echo success"]).and_raise "ENOENT"
-      Object.should_receive(:const_get).with("RUBY_PLATFORM").and_return("x86-mingw")
+      expect(IO).to receive(:popen).with(["sh", "-c", "echo success"]).and_raise "ENOENT"
+      expect(Object).to receive(:const_get).with("RUBY_PLATFORM").and_return("x86-mingw")
       expect(Rscons.get_system_shell).to eq(["cmd", "/c"])
     end
 
     it "uses sh -c on a non-mingw platform if SHELL is not specified" do
       my_ENV = {"SHELL" => nil}
-      ENV.stub(:[]) {|*args| my_ENV[*args]}
-      Object.should_receive(:const_get).with("RUBY_PLATFORM").and_return("x86-linux")
+      allow(ENV).to receive(:[]) {|*args| my_ENV[*args]}
+      expect(Object).to receive(:const_get).with("RUBY_PLATFORM").and_return("x86-linux")
       expect(Rscons.get_system_shell).to eq(["sh", "-c"])
     end
   end
@@ -78,28 +78,28 @@ describe Rscons do
       end
 
       it "returns ['env'] if mingw platform in MSYS and 'env' works" do
-        Object.should_receive(:const_get).and_return("x86-mingw")
-        ENV.should_receive(:keys).and_return(["MSYSCON"])
+        expect(Object).to receive(:const_get).and_return("x86-mingw")
+        expect(ENV).to receive(:keys).and_return(["MSYSCON"])
         io = StringIO.new("success\n")
-        IO.should_receive(:popen).with(["env", "echo", "success"]).and_yield(io)
+        expect(IO).to receive(:popen).with(["env", "echo", "success"]).and_yield(io)
         expect(Rscons.command_executer).to eq(["env"])
       end
 
       it "returns [] if mingw platform in MSYS and 'env' does not work" do
-        Object.should_receive(:const_get).and_return("x86-mingw")
-        ENV.should_receive(:keys).and_return(["MSYSCON"])
-        IO.should_receive(:popen).with(["env", "echo", "success"]).and_raise "ENOENT"
+        expect(Object).to receive(:const_get).and_return("x86-mingw")
+        expect(ENV).to receive(:keys).and_return(["MSYSCON"])
+        expect(IO).to receive(:popen).with(["env", "echo", "success"]).and_raise "ENOENT"
         expect(Rscons.command_executer).to eq([])
       end
 
       it "returns [] if mingw platform not in MSYS" do
-        Object.should_receive(:const_get).and_return("x86-mingw")
-        ENV.should_receive(:keys).and_return(["COMSPEC"])
+        expect(Object).to receive(:const_get).and_return("x86-mingw")
+        expect(ENV).to receive(:keys).and_return(["COMSPEC"])
         expect(Rscons.command_executer).to eq([])
       end
 
       it "returns [] if not mingw platform" do
-        Object.should_receive(:const_get).and_return("x86-linux")
+        expect(Object).to receive(:const_get).and_return("x86-linux")
         expect(Rscons.command_executer).to eq([])
       end
     end