diff --git a/libvips/foreign/vipspng.c b/libvips/foreign/vipspng.c
index 89c65b50..5d980425 100644
--- a/libvips/foreign/vipspng.c
+++ b/libvips/foreign/vipspng.c
@@ -490,6 +490,11 @@ png2vips_header( Read *read, VipsImage *out )
 				return( -1 ); 
 	}
 
+	/* Attach original palette bit depth, if any, as metadata.
+	 */
+	if( color_type == PNG_COLOR_TYPE_PALETTE )
+		vips_image_set_int( out, "palette-bit-depth", bit_depth );
+
 	return( 0 );
 }