diff --git a/lib/libz/Makefile b/lib/libz/Makefile
index 4a6e3c91a828..abc490980deb 100644
--- a/lib/libz/Makefile
+++ b/lib/libz/Makefile
@@ -53,7 +53,6 @@ CFLAGS+=	-DUNALIGNED_OK
 VERSION_DEF=	${.CURDIR}/Versions.def
 SYMBOL_MAPS=	${.CURDIR}/Symbol.map
 CFLAGS+=	-DSYMBOL_VERSIONING
-CFLAGS+=	${NO_WDEPRECATED_NON_PROTOTYPE}
 
 INCS=		zconf.h zlib.h
 
@@ -84,3 +83,5 @@ test: example minigzip
 PCFILES=	zlib.pc
 
 .include <bsd.lib.mk>
+
+CWARNFLAGS+=	${NO_WDEPRECATED_NON_PROTOTYPE}