diff --git a/libavfilter/drawutils.c b/libavfilter/drawutils.c
index 1081938d86..95525d38b4 100644
--- a/libavfilter/drawutils.c
+++ b/libavfilter/drawutils.c
@@ -61,6 +61,7 @@ int ff_fill_rgba_map(uint8_t *rgba_map, enum AVPixelFormat pix_fmt)
 
             had0 |= pos == 0;
             rgba_map[i] = pos;
+            depthb = db;
         }
 
         if (desc->nb_components == 3)