diff --git a/x11/mate/calc/Makefile b/x11/mate/calc/Makefile
index 1392a33e0c7..8f7b6f6d6a8 100644
--- a/x11/mate/calc/Makefile
+++ b/x11/mate/calc/Makefile
@@ -1,4 +1,4 @@
-# $OpenBSD: Makefile,v 1.16 2021/08/25 12:05:51 robert Exp $
+# $OpenBSD: Makefile,v 1.17 2022/01/17 15:18:18 kmos Exp $
 
 COMMENT=		MATE calculator
 
@@ -25,4 +25,9 @@ MODGNOME_TOOLS=		desktop-file-utils yelp
 
 CONFIGURE_STYLE=	gnu
 
+.include <bsd.port.arch.mk>
+.if !${PROPERTIES:Mclang}
+CFLAGS +=	-std=gnu99
+.endif
+
 .include <bsd.port.mk>