diff --git a/databases/ruby-xapian/Makefile b/databases/ruby-xapian/Makefile
index c1c2d98a47fe..12d703ff5566 100644
--- a/databases/ruby-xapian/Makefile
+++ b/databases/ruby-xapian/Makefile
@@ -50,4 +50,10 @@ PORTDOCS=	*
 post-patch:
 	@${REINPLACE_CMD} -e 's|-lstdc++||g' ${WRKSRC}/configure
 
-.include <bsd.port.mk>
+.include <bsd.port.pre.mk>
+
+.if ${RUBY_VER} >= 2.6
+BUILD_DEPENDS+=	rubygem-rdoc>=0:devel/rubygem-rdoc
+.endif
+
+.include <bsd.port.post.mk>