diff --git a/samples/mount_sample/mount.go b/samples/mount_sample/mount.go
index 48f860d..e7d0def 100644
--- a/samples/mount_sample/mount.go
+++ b/samples/mount_sample/mount.go
@@ -17,6 +17,7 @@
 package main
 
 import (
+	"errors"
 	"flag"
 	"fmt"
 	"log"
@@ -30,6 +31,7 @@ import (
 
 var fType = flag.String("type", "", "The name of the samples/ sub-dir.")
 var fMountPoint = flag.String("mount_point", "", "Path to mount point.")
+var fReadyFile = flag.Uint64("ready_file", 0, "FD to signal when ready.")
 
 var fFlushesFile = flag.Uint64("flushfs.flushes_file", 0, "")
 var fFsyncsFile = flag.Uint64("flushfs.fsyncs_file", 0, "")
@@ -97,9 +99,25 @@ func makeFS() (fs fuse.FileSystem, err error) {
 	return
 }
 
+func getReadyFile() (f *os.File, err error) {
+	if *fReadyFile == 0 {
+		err = errors.New("You must set --ready_file.")
+		return
+	}
+
+	f = os.NewFile(uintptr(*fReadyFile), "(ready file)")
+	return
+}
+
 func main() {
 	flag.Parse()
 
+	// Grab the file to signal when ready.
+	readyFile, err := getReadyFile()
+	if err != nil {
+		log.Fatalf("getReadyFile:", err)
+	}
+
 	// Create an appropriate file system.
 	fs, err := makeFS()
 	if err != nil {
@@ -121,6 +139,12 @@ func main() {
 		log.Fatalf("WaitForReady: %v", err)
 	}
 
+	// Signal that it is ready.
+	_, err = readyFile.Write([]byte("x"))
+	if err != nil {
+		log.Fatalf("readyFile.Write: %v", err)
+	}
+
 	// Wait for it to be unmounted.
 	if err = mfs.Join(context.Background()); err != nil {
 		log.Fatalf("Join: %v", err)
diff --git a/samples/subprocess.go b/samples/subprocess.go
index fcfbcdd..acfd97d 100644
--- a/samples/subprocess.go
+++ b/samples/subprocess.go
@@ -24,7 +24,6 @@ import (
 	"os/exec"
 	"path"
 	"sync"
-	"time"
 
 	"github.com/jacobsa/ogletest"
 	"golang.org/x/net/context"
@@ -145,6 +144,16 @@ func waitForMountSample(
 	err = fmt.Errorf("Waiting for mount_sample: %v", err)
 }
 
+func waitForReady(readyReader *os.File, c chan<- struct{}) {
+	_, err := readyReader.Read(make([]byte, 1))
+	if err != nil {
+		log.Printf("Readying from ready pipe: %v", err)
+		return
+	}
+
+	c <- struct{}{}
+}
+
 // Like SetUp, but doens't panic.
 func (t *SubprocessTest) initialize() (err error) {
 	// Initialize the context.
@@ -174,6 +183,18 @@ func (t *SubprocessTest) initialize() (err error) {
 
 	args = append(args, t.MountFlags...)
 
+	// Set up a pipe for the "ready" status.
+	readyReader, readyWriter, err := os.Pipe()
+	if err != nil {
+		err = fmt.Errorf("Pipe: %v", err)
+		return
+	}
+
+	defer readyReader.Close()
+	defer readyWriter.Close()
+
+	t.MountFiles["ready_file"] = readyWriter
+
 	// Set up inherited files and appropriate flags.
 	var extraFiles []*os.File
 	for flag, file := range t.MountFiles {
@@ -199,12 +220,21 @@ func (t *SubprocessTest) initialize() (err error) {
 
 	// Launch a goroutine that waits for it and returns its status.
 	mountSampleErr := make(chan error, 1)
-	t.mountSampleErr = mountSampleErr
 	go waitForMountSample(mountCmd, mountSampleErr, &stderr)
 
-	// TODO(jacobsa): Probably need some sort of signalling (on stderr? write to
-	// a flag-controlled file?) when WaitForReady has returned.
-	time.Sleep(time.Second)
+	// Wait for the tool to say the file system is ready. In parallel, watch for
+	// the tool to fail.
+	readyChan := make(chan struct{}, 1)
+	go waitForReady(readyReader, readyChan)
+
+	select {
+	case <-readyChan:
+	case err = <-mountSampleErr:
+		return
+	}
+
+	// TearDown is no responsible for joining.
+	t.mountSampleErr = mountSampleErr
 
 	return
 }