diff --git a/drivers/gpu/drm/radeon/radeon_atombios.c b/drivers/gpu/drm/radeon/radeon_atombios.c
index f0ea7f8da678f21a516deacc896c12b1543871ad..1fff95505cf5fec08f5506c47e26b8e00866632c 100644
--- a/drivers/gpu/drm/radeon/radeon_atombios.c
+++ b/drivers/gpu/drm/radeon/radeon_atombios.c
@@ -264,6 +264,8 @@ static bool radeon_atom_apply_quirks(struct drm_device *dev,
 		if ((supported_device == ATOM_DEVICE_CRT1_SUPPORT) ||
 		    (supported_device == ATOM_DEVICE_DFP2_SUPPORT))
 			return false;
+		if (supported_device == ATOM_DEVICE_CRT2_SUPPORT)
+			*line_mux = 0x90;
 	}
 
 	/* ASUS HD 3600 XT board lists the DVI port as HDMI */