diff --git a/libtiff/tif_zip.c b/libtiff/tif_zip.c
index c7507734..325222e5 100644
--- a/libtiff/tif_zip.c
+++ b/libtiff/tif_zip.c
@@ -384,6 +384,9 @@ TIFFInitZIP(TIFF* tif, int scheme)
 
 	assert( (scheme == COMPRESSION_DEFLATE)
 		|| (scheme == COMPRESSION_ADOBE_DEFLATE));
+#ifdef NDEBUG
+	(void)scheme;
+#endif
 
 	/*
 	 * Merge codec-specific tag information.