diff --git a/pngrtran.c b/pngrtran.c
index 8b3f785..5c4128d 100644
--- a/pngrtran.c
+++ b/pngrtran.c
@@ -4756,7 +4756,7 @@
 
          else
             png_do_expand(row_info, png_ptr->row_buf + 1,
-                NULL);
+                (png_const_color_16p)NULL);
       }
    }
 #endif