diff --git a/app/gl_ios.go b/app/gl_ios.go
index 31db2541..34d85d1c 100644
--- a/app/gl_ios.go
+++ b/app/gl_ios.go
@@ -115,9 +115,6 @@ func (c *context) Unlock() {
 }
 
 func (c *context) Refresh() error {
-	if C.gio_makeCurrent(c.ctx) == 0 {
-		return errors.New("[EAGLContext setCurrentContext] failed")
-	}
 	if !c.init {
 		c.init = true
 		c.frameBuffer = c.c.CreateFramebuffer()
diff --git a/app/gl_macos.go b/app/gl_macos.go
index 041bcb32..fe77ea0a 100644
--- a/app/gl_macos.go
+++ b/app/gl_macos.go
@@ -111,8 +111,6 @@ func (c *glContext) Unlock() {
 }
 
 func (c *glContext) Refresh() error {
-	c.Lock()
-	defer c.Unlock()
 	C.gio_updateContext(c.ctx)
 	return nil
 }
diff --git a/app/os.go b/app/os.go
index 6da6d34b..cf337985 100644
--- a/app/os.go
+++ b/app/os.go
@@ -165,6 +165,8 @@ type frameEvent struct {
 	Sync bool
 }
 
+// The caller must hold the context lock while using API, Refresh,
+// RenderTarget, or Present.
 type context interface {
 	API() gpu.API
 	RenderTarget() (gpu.RenderTarget, error)
diff --git a/app/window.go b/app/window.go
index 977ab6a1..0e5d04d2 100644
--- a/app/window.go
+++ b/app/window.go
@@ -149,6 +149,12 @@ func (w *Window) validateAndProcess(size image.Point, sync bool, frame *op.Ops,
 				sync = true
 			}
 		}
+		if w.ctx != nil {
+			if err := w.ctx.Lock(); err != nil {
+				w.destroyGPU()
+				return err
+			}
+		}
 		if sync && w.ctx != nil {
 			if err := w.ctx.Refresh(); err != nil {
 				if errors.Is(err, errOutOfDate) {
@@ -163,12 +169,6 @@ func (w *Window) validateAndProcess(size image.Point, sync bool, frame *op.Ops,
 				return err
 			}
 		}
-		if w.ctx != nil {
-			if err := w.ctx.Lock(); err != nil {
-				w.destroyGPU()
-				return err
-			}
-		}
 		if w.gpu == nil && !w.nocontext {
 			gpu, err := gpu.New(w.ctx.API())
 			if err != nil {