diff --git a/libvips/foreign/spngsave.c b/libvips/foreign/spngsave.c
index 445bb3cfa7..c0db1ca88e 100644
--- a/libvips/foreign/spngsave.c
+++ b/libvips/foreign/spngsave.c
@@ -270,7 +270,7 @@ vips_foreign_save_spng_pack( VipsForeignSaveSpng *spng,
 	VipsPel *q, VipsPel *p, size_t n )
 {
         int pixel_mask = 8 / spng->bitdepth - 1;
-	int shift = 8 - spng->bitdepth;
+	int shift = spng->palette ? 0 : 8 - spng->bitdepth;
 
         VipsPel bits;
         size_t x;