diff --git a/asset/asset.go b/asset/asset.go
index d17c0f9..90a2bb2 100644
--- a/asset/asset.go
+++ b/asset/asset.go
@@ -4,18 +4,6 @@
 
 // +build darwin linux
 
-// Package asset provides access to application-bundled assets.
-//
-// On Android, assets are accessed via android.content.res.AssetManager.
-// These files are stored in the assets/ directory of the app. Any raw asset
-// can be accessed by its direct relative name. For example assets/img.png
-// can be opened with Open("img.png").
-//
-// On iOS an asset is a resource stored in the application bundle.
-// Resources can be loaded using the same relative paths.
-//
-// For consistency when debugging on a desktop, assets are read from a
-// directory named assets under the current working directory.
 package asset
 
 import "io"
diff --git a/asset/doc.go b/asset/doc.go
new file mode 100644
index 0000000..37bb9bb
--- /dev/null
+++ b/asset/doc.go
@@ -0,0 +1,17 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package asset provides access to application-bundled assets.
+//
+// On Android, assets are accessed via android.content.res.AssetManager.
+// These files are stored in the assets/ directory of the app. Any raw asset
+// can be accessed by its direct relative name. For example assets/img.png
+// can be opened with Open("img.png").
+//
+// On iOS an asset is a resource stored in the application bundle.
+// Resources can be loaded using the same relative paths.
+//
+// For consistency when debugging on a desktop, assets are read from a
+// directory named assets under the current working directory.
+package asset
diff --git a/bind/java/testpkg/testpkg.go b/bind/java/testpkg/testpkg.go
index fd795e4..4d59c39 100644
--- a/bind/java/testpkg/testpkg.go
+++ b/bind/java/testpkg/testpkg.go
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build darwin linux
+
 // Package testpkg contains bound functions for testing the cgo-JNI interface.
 // This is used in tests of golang.org/x/mobile/bind/java.
 package testpkg
diff --git a/example/audio/main_x.go b/example/audio/main_x.go
new file mode 100644
index 0000000..e528533
--- /dev/null
+++ b/example/audio/main_x.go
@@ -0,0 +1,10 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !darwin,!linux
+
+package main
+
+func main() {
+}
diff --git a/example/basic/main_x.go b/example/basic/main_x.go
new file mode 100644
index 0000000..3d440e7
--- /dev/null
+++ b/example/basic/main_x.go
@@ -0,0 +1,10 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !darwin,!linux
+
+package main
+
+func main() {
+}
diff --git a/example/network/main_x.go b/example/network/main_x.go
new file mode 100644
index 0000000..e528533
--- /dev/null
+++ b/example/network/main_x.go
@@ -0,0 +1,10 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !darwin,!linux
+
+package main
+
+func main() {
+}
diff --git a/example/sprite/main_x.go b/example/sprite/main_x.go
new file mode 100644
index 0000000..3d440e7
--- /dev/null
+++ b/example/sprite/main_x.go
@@ -0,0 +1,10 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !darwin,!linux
+
+package main
+
+func main() {
+}
diff --git a/exp/app/debug/fps.go b/exp/app/debug/fps.go
index fbd371b..d90d60f 100644
--- a/exp/app/debug/fps.go
+++ b/exp/app/debug/fps.go
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build darwin linux
+
 // Package debug provides GL-based debugging tools for apps.
 package debug // import "golang.org/x/mobile/exp/app/debug"
 
diff --git a/exp/gl/glutil/doc.go b/exp/gl/glutil/doc.go
new file mode 100644
index 0000000..44b1210
--- /dev/null
+++ b/exp/gl/glutil/doc.go
@@ -0,0 +1,6 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package glutil implements OpenGL utility functions.
+package glutil // import "golang.org/x/mobile/exp/gl/glutil"
diff --git a/exp/gl/glutil/glutil.go b/exp/gl/glutil/glutil.go
index babb1c9..2ac6c87 100644
--- a/exp/gl/glutil/glutil.go
+++ b/exp/gl/glutil/glutil.go
@@ -2,7 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package glutil implements OpenGL utility functions.
+// +build darwin linux
+
 package glutil // import "golang.org/x/mobile/exp/gl/glutil"
 
 import (
diff --git a/exp/sensor/sensor.go b/exp/sensor/sensor.go
index 8e93feb..8745c29 100644
--- a/exp/sensor/sensor.go
+++ b/exp/sensor/sensor.go
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build darwin linux
+
 // Package sensor provides sensor events from various movement sensors.
 package sensor // import "golang.org/x/mobile/exp/sensor"
 
diff --git a/exp/sprite/glsprite/glsprite.go b/exp/sprite/glsprite/glsprite.go
index 6d1395a..b335996 100644
--- a/exp/sprite/glsprite/glsprite.go
+++ b/exp/sprite/glsprite/glsprite.go
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build darwin linux
+
 // Package glsprite implements a sprite Engine using OpenGL ES 2.
 //
 // Each sprite.Texture is loaded as a GL texture object and drawn
diff --git a/gl/work.c b/gl/work.c
index cdea4e5..eb5802b 100644
--- a/gl/work.c
+++ b/gl/work.c
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build darwin linux
+
 #include <stdlib.h>
 #include "_cgo_export.h"
 #include "work.h"