diff --git a/cmd/gogio/e2e_test.go b/cmd/gogio/e2e_test.go
index eb542cf4..e2ee5646 100644
--- a/cmd/gogio/e2e_test.go
+++ b/cmd/gogio/e2e_test.go
@@ -21,7 +21,7 @@ type TestDriver interface {
 	// white.
 	//
 	// When the function returns, the gio app must be ready to use on the
-	// platform.
+	// platform, with its initial frame fully drawn.
 	//
 	// The returned cleanup funcs must be run in reverse order, to mimic
 	// deferred funcs.
@@ -32,7 +32,8 @@ type TestDriver interface {
 	Screenshot() image.Image
 
 	// Click performs a pointer click at the specified coordinates,
-	// including both press and release.
+	// including both press and release. It returns when the next frame is
+	// fully drawn.
 	Click(x, y int)
 }
 
diff --git a/cmd/gogio/testdata/red.go b/cmd/gogio/testdata/red.go
index 0450cf3b..9e59e1d0 100644
--- a/cmd/gogio/testdata/red.go
+++ b/cmd/gogio/testdata/red.go
@@ -4,9 +4,11 @@
 package main
 
 import (
+	"fmt"
 	"image"
 	"image/color"
 	"log"
+	"runtime"
 
 	"gioui.org/app"
 	"gioui.org/f32"
@@ -26,6 +28,18 @@ func main() {
 	app.Main()
 }
 
+type notifyFrame int
+
+const (
+	notifyNone notifyFrame = iota
+	notifyInvalidate
+	notifyPrint
+)
+
+// notify keeps track of whether we want to print to stdout to notify the user
+// when a frame is ready. Initially we want to notify about the first frame.
+var notify = notifyInvalidate
+
 func loop(w *app.Window) error {
 	topLeft := quarterWidget{
 		color: color.RGBA{R: 0xde, G: 0xad, B: 0xbe, A: 0xff},
@@ -67,6 +81,22 @@ func loop(w *app.Window) error {
 			rows.Layout(gtx, r1, r2)
 
 			e.Frame(gtx.Ops)
+
+			if runtime.GOOS == "js" {
+				// TODO(mvdan): Unfortunately, printing to
+				// stdout crashes the js/wasm port. Use the
+				// prints once the issue is fixed:
+				// https://github.com/golang/go/issues/35256
+				break
+			}
+			switch notify {
+			case notifyInvalidate:
+				notify = notifyPrint
+				w.Invalidate()
+			case notifyPrint:
+				notify = notifyNone
+				fmt.Println("frame ready")
+			}
 		}
 	}
 }
@@ -100,6 +130,8 @@ func (w *quarterWidget) Layout(gtx *layout.Context) {
 	for _, e := range gtx.Events(w) {
 		if e, ok := e.(pointer.Event); ok && e.Type == pointer.Press {
 			w.clicked = !w.clicked
+			// notify when we're done updating the frame.
+			notify = notifyInvalidate
 		}
 	}
 }
diff --git a/cmd/gogio/x11_test.go b/cmd/gogio/x11_test.go
index 72113b0b..5b772312 100644
--- a/cmd/gogio/x11_test.go
+++ b/cmd/gogio/x11_test.go
@@ -7,6 +7,7 @@
 package main_test
 
 import (
+	"bufio"
 	"bytes"
 	"context"
 	"fmt"
@@ -26,10 +27,13 @@ import (
 type X11TestDriver struct {
 	t *testing.T
 
+	frameNotifs chan bool
+
 	display string
 }
 
 func (d *X11TestDriver) Start(t_ *testing.T, path string, width, height int) (cleanups []func()) {
+	d.frameNotifs = make(chan bool, 1)
 	d.t = t_
 
 	// Pick a random display number between 1 and 100,000. Most machines
@@ -125,10 +129,14 @@ func (d *X11TestDriver) Start(t_ *testing.T, path string, width, height int) (cl
 	{
 		ctx, cancel := context.WithCancel(context.Background())
 		cmd := exec.CommandContext(ctx, bin)
-		out := &bytes.Buffer{}
 		cmd.Env = []string{"DISPLAY=" + d.display}
-		cmd.Stdout = out
-		cmd.Stderr = out
+		stdout, err := cmd.StdoutPipe()
+		if err != nil {
+			d.t.Fatal(err)
+		}
+		stderr := &bytes.Buffer{}
+		cmd.Stderr = stderr
+
 		if err := cmd.Start(); err != nil {
 			d.t.Fatal(err)
 		}
@@ -136,17 +144,26 @@ func (d *X11TestDriver) Start(t_ *testing.T, path string, width, height int) (cl
 		wg.Add(1)
 		go func() {
 			if err := cmd.Wait(); err != nil && ctx.Err() == nil {
-				// Print all output and error.
-				io.Copy(os.Stdout, out)
+				// Print stderr and error.
+				io.Copy(os.Stdout, stderr)
 				d.t.Error(err)
 			}
 			wg.Done()
 		}()
+		go func() {
+			scanner := bufio.NewScanner(stdout)
+			for scanner.Scan() {
+				line := scanner.Text()
+				if line == "frame ready" {
+					d.frameNotifs <- true
+				}
+			}
+		}()
+
 	}
 
 	// Wait for the gio app to render.
-	// TODO(mvdan): synchronize with the app instead
-	time.Sleep(400 * time.Millisecond)
+	<-d.frameNotifs
 
 	return cleanups
 }
@@ -183,8 +200,7 @@ func (d *X11TestDriver) Click(x, y int) {
 	d.xdotool("mousemove", x, y)
 	d.xdotool("click", "1")
 
-	// TODO(mvdan): synchronize with the app instead
-	time.Sleep(200 * time.Millisecond)
+	<-d.frameNotifs
 }
 
 func TestX11(t *testing.T) {