Antoine suggested putting the version number in a variable. A revised tarball is attached.
--- Makefile.orig Fri Jun 12 17:15:13 2015
+++ Makefile Sat Jun 13 07:51:58 2015
@@ -1,7 +1,8 @@
# $OpenBSD
COMMENT = frontend to the popular Tarsnap backup service
-DISTNAME = tarsnap-gui-0.5
+V = 0.5
+DISTNAME = tarsnap-gui-${V}
CATEGORIES = sysutils
HOMEPAGE = https://github.com/Tarsnap/tarsnap-gui/wiki/Tarsnap
@@ -15,7 +16,7 @@
GH_ACCOUNT = Tarsnap
GH_PROJECT = tarsnap-gui
-GH_TAGNAME = v0.5
+GH_TAGNAME = v${V}
MODULES = x11/qt5
RUN_DEPENDS = sysutils/tarsnap
tarsnap-gui.tar.gz
Description: application/tar-gz
