diff --git a/internal/ui/monitor_glfw.go b/internal/ui/monitor_glfw.go
index 7897056c8..a3580affe 100644
--- a/internal/ui/monitor_glfw.go
+++ b/internal/ui/monitor_glfw.go
@@ -79,16 +79,15 @@ func (m *monitors) append(ms []*Monitor) []*Monitor {
 	return append(ms, m.monitors...)
 }
 
-func (m *monitors) monitorFromGLFWMonitor(glfwMonitor *glfw.Monitor) *Monitor {
+func (m *monitors) primaryMonitor() *Monitor {
+	if atomic.LoadInt32(&m.updateCalled) == 0 {
+		panic("ui: (*monitors).primaryMonitor must be called before (*monitors).append is called")
+	}
+
 	m.m.Lock()
 	defer m.m.Unlock()
 
-	for _, m := range m.monitors {
-		if m.m == glfwMonitor {
-			return m
-		}
-	}
-	return nil
+	return m.monitors[0]
 }
 
 func (m *monitors) monitorFromID(id int) *Monitor {
diff --git a/internal/ui/ui_glfw.go b/internal/ui/ui_glfw.go
index 9d7c02c5e..7ccc354c1 100644
--- a/internal/ui/ui_glfw.go
+++ b/internal/ui/ui_glfw.go
@@ -172,7 +172,7 @@ func initialize() error {
 		return err
 	}
 	if m == nil {
-		m = theMonitors.monitorFromGLFWMonitor(glfw.GetPrimaryMonitor())
+		m = theMonitors.primaryMonitor()
 	}
 
 	// GetPrimaryMonitor might return nil in theory (#1887).
@@ -1479,7 +1479,7 @@ func (u *userInterfaceImpl) currentMonitor() *Monitor {
 		return m
 	}
 
-	return theMonitors.monitorFromGLFWMonitor(glfw.GetPrimaryMonitor())
+	return theMonitors.primaryMonitor()
 }
 
 func (u *userInterfaceImpl) readInputState(inputState *InputState) {
diff --git a/internal/ui/ui_glfw_darwin.go b/internal/ui/ui_glfw_darwin.go
index 5dc3eedd7..05e6cf12f 100644
--- a/internal/ui/ui_glfw_darwin.go
+++ b/internal/ui/ui_glfw_darwin.go
@@ -239,7 +239,7 @@ var (
 	sel_windowWillExitFullScreen      = objc.RegisterName("windowWillExitFullScreen:")
 )
 
-func currentMouseLocation() (x, y int) {
+func currentMouseLocationInDIP() (x, y int) {
 	sig := cocoa.NSMethodSignature_signatureWithObjCTypes("{NSPoint=dd}@:")
 	inv := cocoa.NSInvocation_invocationWithMethodSignature(sig)
 	inv.SetTarget(objc.ID(class_NSEvent))
@@ -247,11 +247,20 @@ func currentMouseLocation() (x, y int) {
 	inv.Invoke()
 	var point cocoa.NSPoint
 	inv.GetReturnValue(unsafe.Pointer(&point))
-	return int(point.X), int(point.Y)
+
+	// On macOS, the unit of GLFW (OS-native) pixels' scale and device-independent pixels's scale are the same.
+	// The monitor sizes' scales are also the same.
+	x, y = int(point.X), int(point.Y)
+
+	// On macOS, the Y axis is upward. Adjust the Y position (#807, #2794).
+	y = -y
+	m := theMonitors.primaryMonitor()
+	y += m.videoMode.Height
+	return x, y
 }
 
 func initialMonitorByOS() (*Monitor, error) {
-	x, y := currentMouseLocation()
+	x, y := currentMouseLocationInDIP()
 
 	// Find the monitor including the cursor.
 	for _, m := range theMonitors.append(nil) {