diff --git a/src/atombios_crtc.c b/src/atombios_crtc.c
index f9698f3..65afd00 100644
--- a/src/atombios_crtc.c
+++ b/src/atombios_crtc.c
@@ -324,6 +324,10 @@ atombios_crtc_set_pll(xf86CrtcPtr crtc, DisplayModePtr mode)
 	else
 	    pll_flags |= RADEON_PLL_PREFER_LOW_REF_DIV;
 
+	if ((info->ChipFamily == CHIP_FAMILY_RS780) ||
+	    (info->ChipFamily == CHIP_FAMILY_RS880))
+	    pll_flags |= RADEON_PLL_USE_FRAC_FB_DIV;
+
 	for (i = 0; i < xf86_config->num_output; i++) {
 	    xf86OutputPtr output = xf86_config->output[i];
 	    if (output->crtc == crtc) {