diff --git a/webrtc/modules/desktop_capture/screen_capturer_mac.mm b/webrtc/modules/desktop_capture/screen_capturer_mac.mm
index 8ec4ccedfa..b652477273 100644
--- a/webrtc/modules/desktop_capture/screen_capturer_mac.mm
+++ b/webrtc/modules/desktop_capture/screen_capturer_mac.mm
@@ -463,7 +463,7 @@ void ScreenCapturerMac::GlBlitFast(const DesktopFrame& frame,
 
     // Since the image obtained from OpenGL is upside-down, need to do some
     // magic here to copy the correct rectangle.
-    const int y_offset = (frame.size().width() - 1) * frame.stride();
+    const int y_offset = (frame.size().height() - 1) * frame.stride();
     for (DesktopRegion::Iterator i(last_invalid_region_);
          !i.IsAtEnd(); i.Advance()) {
       DesktopRect copy_rect = i.rect();