diff --git a/hw/xfree86/modes/xf86EdidModes.c b/hw/xfree86/modes/xf86EdidModes.c
index 2f26a64..9489947 100644
--- a/hw/xfree86/modes/xf86EdidModes.c
+++ b/hw/xfree86/modes/xf86EdidModes.c
@@ -327,6 +327,12 @@ DDCModeFromDetailedTiming(int scrnIndex, struct detailed_timings *timing,
     Mode->VSyncEnd = Mode->VSyncStart + timing->v_sync_width;
     Mode->VTotal = timing->v_active + timing->v_blanking;
 
+    /* perform basic check on the detail timing */
+    if (Mode->HSyncEnd > Mode->HTotal || Mode->VSyncEnd > Mode->VTotal) {
+	xfree(Mode);
+	return NULL;
+    }
+
     xf86SetModeDefaultName(Mode);
 
     /* We ignore h/v_size and h/v_border for now. */