diff --git a/lib/libz/Makefile b/lib/libz/Makefile
index abc490980de..734da7fa539 100644
--- a/lib/libz/Makefile
+++ b/lib/libz/Makefile
@@ -84,4 +84,4 @@ PCFILES=	zlib.pc
 
 .include <bsd.lib.mk>
 
-CWARNFLAGS+=	${NO_WDEPRECATED_NON_PROTOTYPE}
+CWARNFLAGS+=	${NO_WDEPRECATED_NON_PROTOTYPE} ${NO_WSTRICT_PROTOTYPES}