diff --git a/panda/src/tinydisplay/ztriangle.h b/panda/src/tinydisplay/ztriangle.h
index 0c7cb0d7aa..dd5e6bb0b6 100644
--- a/panda/src/tinydisplay/ztriangle.h
+++ b/panda/src/tinydisplay/ztriangle.h
@@ -353,6 +353,7 @@
 	r1+=drdl_min;
 	g1+=dgdl_min;
 	b1+=dbdl_min;
+	a1+=dadl_min;
 #endif
 #ifdef INTERP_ST
 	s1+=dsdl_min;