diff --git a/build_tests/simple/absolute_source_path.rb b/build_tests/simple/absolute_source_path.rb
new file mode 100644
index 0000000..2b1f812
--- /dev/null
+++ b/build_tests/simple/absolute_source_path.rb
@@ -0,0 +1,14 @@
+Rscons::Environment.new do |env|
+  env.build_root = "build"
+  tempdir = ENV["TEMP"] || ENV["TMP"] || "/tmp"
+  source_file = File.join(tempdir, "abs.c")
+  File.open(source_file, "w") do |fh|
+    fh.puts(<<-EOF)
+    int main()
+    {
+      return 29;
+    }
+    EOF
+  end
+  env.Program("abs.exe", source_file)
+end
diff --git a/lib/rscons.rb b/lib/rscons.rb
index 02f6e0e..7af226f 100644
--- a/lib/rscons.rb
+++ b/lib/rscons.rb
@@ -71,7 +71,11 @@ module Rscons
     #
     # @return [Boolean] Whether the given path is an absolute filesystem path.
     def absolute_path?(path)
-      path =~ %r{^(/|\w:[\\/])}
+      if RUBY_PLATFORM =~ /mingw/
+        path =~ %r{^(?:\w:)?[\\/]}
+      else
+        path.start_with?("/")
+      end
     end
 
     # Return whether the given target is a phony target.
diff --git a/lib/rscons/environment.rb b/lib/rscons/environment.rb
index f120e02..4f0bd74 100644
--- a/lib/rscons/environment.rb
+++ b/lib/rscons/environment.rb
@@ -245,12 +245,17 @@ module Rscons
         end
       end
       if @build_root and not found_match
-        unless Rscons.absolute_path?(source_fname) or build_fname.start_with?("#{@build_root}/")
+        if Rscons.absolute_path?(build_fname)
+          if build_fname =~ %r{^(\w):(.*)$}
+            build_fname = "#{@build_root}/_#{$1}#{$2}"
+          else
+            build_fname = "#{@build_root}/_#{build_fname}"
+          end
+        elsif !build_fname.start_with?("#{@build_root}/")
           build_fname = "#{@build_root}/#{build_fname}"
         end
       end
-      build_fname.gsub!('\\', '/')
-      build_fname
+      build_fname.gsub('\\', '/')
     end
 
     # Get a construction variable's value.
diff --git a/spec/build_tests_spec.rb b/spec/build_tests_spec.rb
index 3b61882..d4f7149 100644
--- a/spec/build_tests_spec.rb
+++ b/spec/build_tests_spec.rb
@@ -662,6 +662,15 @@ EOF
     ]
   end
 
+  it "creates object files under the build root for absolute source paths" do
+    test_dir("simple")
+    result = run_test(rsconsfile: "absolute_source_path.rb")
+    expect(result.stderr).to eq ""
+    slines = lines(result.stdout)
+    expect(slines[0]).to match(%r{^CC build/.*/abs\.o$})
+    expect(slines[1]).to eq "LD abs.exe"
+  end
+
   context "backward compatibility" do
     it "allows a builder to call Environment#run_builder in a non-threaded manner" do
       test_dir("simple")
diff --git a/spec/rscons/environment_spec.rb b/spec/rscons/environment_spec.rb
index a11dde1..0d31220 100644
--- a/spec/rscons/environment_spec.rb
+++ b/spec/rscons/environment_spec.rb
@@ -91,12 +91,13 @@ module Rscons
         end
 
         context "with a build_root" do
-          it "uses the build_root unless the path is absolute" do
+          it "uses the build_root" do
+            stub_const("RUBY_PLATFORM", "mingw")
             env = Environment.new
             env.build_root = "build/proj"
             expect(env.get_build_fname("src/dir/file.c", ".o")).to eq "build/proj/src/dir/file.o"
-            expect(env.get_build_fname("/some/lib.c", ".a")).to eq "/some/lib.a"
-            expect(env.get_build_fname("C:\\abspath\\mod.cc", ".o")).to eq "C:/abspath/mod.o"
+            expect(env.get_build_fname("/some/lib.c", ".a")).to eq "build/proj/_/some/lib.a"
+            expect(env.get_build_fname("C:\\abspath\\mod.cc", ".o")).to eq "build/proj/_C/abspath/mod.o"
             expect(env.get_build_fname("build\\proj\\generated.c", ".o")).to eq "build/proj/generated.o"
             expect(env.get_build_fname("build/proj.XX", ".yy")).to eq "build/proj/build/proj.yy"
           end
diff --git a/spec/rscons_spec.rb b/spec/rscons_spec.rb
index 6468f9e..7170e8d 100644
--- a/spec/rscons_spec.rb
+++ b/spec/rscons_spec.rb
@@ -24,6 +24,34 @@ describe Rscons do
     end
   end
 
+  describe ".absolute_path?" do
+    context "on Windows" do
+      it "returns whether a path is absolute" do
+        stub_const("RUBY_PLATFORM", "mingw")
+        expect(Rscons.absolute_path?("/foo")).to be_truthy
+        expect(Rscons.absolute_path?("\\Windows")).to be_truthy
+        expect(Rscons.absolute_path?("C:\\Windows")).to be_truthy
+        expect(Rscons.absolute_path?("f:\\stuff")).to be_truthy
+        expect(Rscons.absolute_path?("g:/projects")).to be_truthy
+        expect(Rscons.absolute_path?("x:foo")).to be_falsey
+        expect(Rscons.absolute_path?("file.txt")).to be_falsey
+      end
+    end
+
+    context "not on Windows" do
+      it "returns whether a path is absolute" do
+        stub_const("RUBY_PLATFORM", "linux")
+        expect(Rscons.absolute_path?("/foo")).to be_truthy
+        expect(Rscons.absolute_path?("\\Windows")).to be_falsey
+        expect(Rscons.absolute_path?("C:\\Windows")).to be_falsey
+        expect(Rscons.absolute_path?("f:\\stuff")).to be_falsey
+        expect(Rscons.absolute_path?("g:/projects")).to be_falsey
+        expect(Rscons.absolute_path?("x:foo")).to be_falsey
+        expect(Rscons.absolute_path?("file.txt")).to be_falsey
+      end
+    end
+  end
+
   describe ".set_suffix" do
     it "changes the suffix to the new one" do
       expect(Rscons.set_suffix("foo.c", ".h")).to eq("foo.h")