diff --git a/pngpriv.h b/pngpriv.h
index ad0ef80..92428b8 100644
--- a/pngpriv.h
+++ b/pngpriv.h
@@ -823,8 +823,10 @@
 PNG_EXTERN void png_do_scale_16_to_8 PNGARG((png_row_infop row_info,
     png_bytep row));
 
+#ifdef PNG_READ_CHOP_16_TO_8_SUPPORTED
 PNG_EXTERN void png_do_chop PNGARG((png_row_infop row_info,
     png_bytep row));
+#endif
 PNG_EXTERN void png_do_scale_16_to_8 PNGARG((png_row_infop row_info,
     png_bytep row));
 #endif