diff --git a/drivers/gpu/drm/radeon/atombios_crtc.c b/drivers/gpu/drm/radeon/atombios_crtc.c
index dab06fb..f5819ba 100644
--- a/drivers/gpu/drm/radeon/atombios_crtc.c
+++ b/drivers/gpu/drm/radeon/atombios_crtc.c
@@ -815,6 +815,8 @@
 			args.v3.ucPostDiv = post_div;
 			args.v3.ucPpll = pll_id;
 			args.v3.ucMiscInfo = (pll_id << 2);
+			if (ss_enabled && (ss->type & ATOM_EXTERNAL_SS_MASK))
+				args.v3.ucMiscInfo |= PIXEL_CLOCK_MISC_REF_DIV_SRC;
 			args.v3.ucTransmitterId = encoder_id;
 			args.v3.ucEncoderMode = encoder_mode;
 			break;