diff --git a/sys/dev/drm/drm_modes.c b/sys/dev/drm/drm_modes.c
--- a/sys/dev/drm/drm_modes.c
+++ b/sys/dev/drm/drm_modes.c
@@ -1126,6 +1126,10 @@
 	    mode->vtotal < mode->vsync_end)
 		return MODE_V_ILLEGAL;
 
+	/* vscan multiplies crtc_v*; cap to avoid signed int overflow */
+	if (mode->vscan > 1 && mode->vscan > UINT_MAX / max(mode->vtotal, 1U))
+		return MODE_V_ILLEGAL;
+
 	return MODE_OK;
 }