diff --git a/build.pl b/build.pl
index 43a7f8bc5..da0d633fc 100755
--- a/build.pl
+++ b/build.pl
@@ -359,6 +359,19 @@ sub build {
     v("Built '$target'");
 }
 
+sub filter_go_os {
+    my @good;
+    my $is_windows = $^O eq "msys" || $^O eq "MSWin32";
+    foreach my $f (@_) {
+        my $for_unix = $f =~ /_unix\.go$/;
+        my $for_windows = $f =~ /_windows\.go$/;
+        next if $for_unix && $is_windows;
+        next if $for_windows && !$is_windows;
+        push @good, $f;
+    }
+    return @good;
+}
+
 sub find_go_camli_deps {
     my $target = shift;
     if ($target =~ /\bthird_party\b/) {
@@ -375,6 +388,7 @@ sub find_go_camli_deps {
     my $target_dir = dir($target);
     opendir(my $dh, $target_dir) or die "Failed to open directory: $target\n";
     my @go_files = grep { !m!^\.\#! } grep { !/_testmain\.go$/ } grep { /\.go$/ } readdir($dh);
+    @go_files = filter_go_os(@go_files);
     closedir($dh);
 
     # TODO: just stat the files first and keep a cache file of the
@@ -439,6 +453,7 @@ sub gen_target_makefile {
     opendir(my $dh, $target_dir) or die;
     my @dir_files = readdir($dh);
     my @go_files = grep { !m!^\.\#! } grep { !/_testmain\.go$/ } grep { /\.go$/ } @dir_files;
+    @go_files = filter_go_os(@go_files);
     closedir($dh);
 
     if ($t->{tags}{fileembed}) {
diff --git a/lib/go/camli/webserver/envpipe_unix.go b/lib/go/camli/webserver/envpipe_unix.go
new file mode 100644
index 000000000..cba422314
--- /dev/null
+++ b/lib/go/camli/webserver/envpipe_unix.go
@@ -0,0 +1,36 @@
+/*
+Copyright 2011 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package webserver
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strconv"
+)
+
+func pipeFromEnvFd(env string) (*os.File, os.Error) {
+	fdStr := os.Getenv(env)
+	if fdStr == "" {
+		return nil, fmt.Errorf("Environment variable %q was blank", env)
+	}
+	fd, err := strconv.Atoi(fdStr)
+	if err != nil {
+		log.Fatalf("Bogus test harness fd '%s': %v", fdStr, err)
+	}
+	return os.NewFile(fd, "testingpipe-"+env), nil
+}
diff --git a/lib/go/camli/webserver/envpipe_windows.go b/lib/go/camli/webserver/envpipe_windows.go
new file mode 100644
index 000000000..f44da5942
--- /dev/null
+++ b/lib/go/camli/webserver/envpipe_windows.go
@@ -0,0 +1,25 @@
+/*
+Copyright 2011 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package webserver
+
+import (
+	"os"
+)
+
+func pipeFromEnvFd(env string) (*os.File, os.Error) {
+	return nil, os.NewError("not implemented")
+}
diff --git a/lib/go/camli/webserver/webserver.go b/lib/go/camli/webserver/webserver.go
index a4c78b263..646d6830f 100644
--- a/lib/go/camli/webserver/webserver.go
+++ b/lib/go/camli/webserver/webserver.go
@@ -25,7 +25,6 @@ import (
 	"log"
 	"net"
 	"os"
-	"strconv"
 	"strings"
 	"time"
 )
@@ -135,24 +134,16 @@ func (s *Server) Serve() {
 }
 
 
-func pipeFromEnvFd(env string) *os.File {
-	fdStr := os.Getenv(env)
-	if fdStr == "" {
-		return nil
-	}
-	fd, err := strconv.Atoi(fdStr)
-	if err != nil {
-		log.Fatalf("Bogus test harness fd '%s': %v", fdStr, err)
-	}
-	return os.NewFile(fd, "testingpipe-"+env)
-}
 
 // Signals the test harness that we've started listening.
 // TODO: write back the port number that we randomly selected?
 // For now just writes back a single byte.
 func runTestHarnessIntegration(listener net.Listener) {
-	writePipe := pipeFromEnvFd("TESTING_PORT_WRITE_FD")
-	readPipe := pipeFromEnvFd("TESTING_CONTROL_READ_FD")
+	writePipe, err := pipeFromEnvFd("TESTING_PORT_WRITE_FD")
+	if err != nil {
+		return
+	}
+	readPipe, _ := pipeFromEnvFd("TESTING_CONTROL_READ_FD")
 
 	if writePipe != nil {
 		writePipe.Write([]byte(listener.Addr().String() + "\n"))