diff --git a/src/mame/trs/coco3.cpp b/src/mame/trs/coco3.cpp
index d3dae6e1711..c5f3db9674e 100644
--- a/src/mame/trs/coco3.cpp
+++ b/src/mame/trs/coco3.cpp
@@ -311,7 +311,7 @@ void coco3_state::coco3(machine_config &config)
 
 	// monitor
 	SCREEN(config, m_screen, SCREEN_TYPE_RASTER);
-	m_screen->set_raw(28.636363_MHz_XTAL/2, 912, 0, 640-1, 262, 1, 241-1);
+	m_screen->set_raw(28.636363_MHz_XTAL/2, 912, 0, 640, 262, 1, 241-1);
 	m_screen->set_screen_update(FUNC(coco3_state::screen_update));
 
 	// internal ram