diff --git a/make.go b/make.go
index 0f954f913..f77113e3f 100644
--- a/make.go
+++ b/make.go
@@ -49,6 +49,7 @@ var (
 	targets        = flag.String("targets", "", "Optional comma-separated list of targets (i.e go packages) to build and install. Empty means all. Example: camlistore.org/server/camlistored,camlistore.org/cmd/camput")
 	quiet          = flag.Bool("quiet", false, "Don't print anything unless there's a failure.")
 	ifModsSince    = flag.Int64("if_mods_since", 0, "If non-zero return immediately without building if there aren't any filesystem modifications past this time (in unix seconds)")
+	buildOS        = flag.String("os", runtime.GOOS, "Operating system to build for.")
 )
 
 var (
@@ -70,6 +71,18 @@ func main() {
 	}
 	verifyCamlistoreRoot(camRoot)
 
+	if runtime.GOOS != *buildOS {
+		if *wantSQLite {
+			log.Fatalf("SQLite isn't available when cross-compiling to another OS. Set --sqlite=false.")
+		}
+		// TODO(bradfitz): we can fix this one, though, by
+		// building genfileembed with the GOOS of the host
+		// instead:
+		if *embedResources {
+			log.Fatalf("Due to a bug, can't currently cross-compile and also embed resources. For now, set --embed_static=false")
+		}
+	}
+
 	sql := *wantSQLite && haveSQLite()
 
 	buildBaseDir := "build-gopath"
@@ -176,7 +189,7 @@ func main() {
 	}
 	args := append(baseArgs, targs...)
 	if buildAll {
-		switch runtime.GOOS {
+		switch *buildOS {
 		case "linux", "darwin":
 			args = append(args, "camlistore.org/cmd/cammount")
 		}
@@ -195,9 +208,7 @@ func main() {
 		cmd.Stderr = os.Stderr
 	}
 	if *verbose {
-		// TODO(reviewer) should this be cmd.Args too? Providing the contents
-		// of baseArgs doesn't hurt when you're trying to debug.
-		log.Printf("Running go install of main binaries with args %s", targs)
+		log.Printf("Running go install of main binaries with args %s", cmd.Args)
 	}
 	if err := cmd.Run(); err != nil {
 		log.Fatalf("Error building main binaries: %v\n%s", err, output.String())
@@ -242,6 +253,9 @@ func cleanGoEnv() (clean []string) {
 		}
 		clean = append(clean, env)
 	}
+	if *buildOS != runtime.GOOS {
+		clean = append(clean, "GOOS="+*buildOS)
+	}
 	return
 }
 
diff --git a/pkg/fs/fs.go b/pkg/fs/fs.go
index e52e41463..5f5cc22c0 100644
--- a/pkg/fs/fs.go
+++ b/pkg/fs/fs.go
@@ -1,3 +1,5 @@
+// +build linux darwin
+
 /*
 Copyright 2011 Google Inc.
 
diff --git a/pkg/fs/recent.go b/pkg/fs/recent.go
index 346617bf1..eb460cef3 100644
--- a/pkg/fs/recent.go
+++ b/pkg/fs/recent.go
@@ -1,3 +1,5 @@
+// +build linux darwin
+
 /*
 Copyright 2013 Google Inc.
 
diff --git a/pkg/fs/root.go b/pkg/fs/root.go
index de81f8af1..7af00489e 100644
--- a/pkg/fs/root.go
+++ b/pkg/fs/root.go
@@ -1,3 +1,5 @@
+// +build linux darwin
+
 /*
 Copyright 2012 Google Inc.
 
diff --git a/third_party/code.google.com/p/rsc/fuse/fuse.go b/third_party/code.google.com/p/rsc/fuse/fuse.go
index e02f4fc3b..faa9b57fa 100644
--- a/third_party/code.google.com/p/rsc/fuse/fuse.go
+++ b/third_party/code.google.com/p/rsc/fuse/fuse.go
@@ -1,3 +1,5 @@
+// +build linux darwin
+
 // Copyright 2011 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.
diff --git a/third_party/code.google.com/p/rsc/fuse/fuse_kernel.go b/third_party/code.google.com/p/rsc/fuse/fuse_kernel.go
index a57360e63..4e6df7fd6 100644
--- a/third_party/code.google.com/p/rsc/fuse/fuse_kernel.go
+++ b/third_party/code.google.com/p/rsc/fuse/fuse_kernel.go
@@ -1,3 +1,5 @@
+// +build linux darwin
+
 // Copyright 2011 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.
diff --git a/third_party/code.google.com/p/rsc/fuse/serve.go b/third_party/code.google.com/p/rsc/fuse/serve.go
index fa4f27e3f..2dd41711f 100644
--- a/third_party/code.google.com/p/rsc/fuse/serve.go
+++ b/third_party/code.google.com/p/rsc/fuse/serve.go
@@ -1,3 +1,5 @@
+// +build linux darwin
+
 // Copyright 2012 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.
diff --git a/third_party/code.google.com/p/rsc/fuse/tree.go b/third_party/code.google.com/p/rsc/fuse/tree.go
index fec0a748f..f42c251c6 100644
--- a/third_party/code.google.com/p/rsc/fuse/tree.go
+++ b/third_party/code.google.com/p/rsc/fuse/tree.go
@@ -1,3 +1,5 @@
+// +build linux darwin
+
 // Copyright 2012 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.