diff --git a/perftest.spec b/perftest.spec
index 4cf3a42..b9fb2cb 100644
--- a/perftest.spec
+++ b/perftest.spec
@@ -1,10 +1,10 @@
 Name:           perftest
 Summary:        IB Performance Tests
 # Upstream uses a dash in the version. Not valid in the Version field, so we use a dot instead.
+# Issue "Please avoid dashes in version":
+#   https://github.com/linux-rdma/perftest/issues/18
 %global upstream_ver 4.5-0.20
-# The directory in the tarball has only the part before the dash.
-%global tarball_ver 4.5
-Version:        4.5.0.20
+Version:        %{lua: v=string.gsub(rpm.expand("%{upstream_ver}"),"-","."); print(v)}
 Release:        %autorelease
 License:        GPLv2 or BSD
 Source:         https://github.com/linux-rdma/perftest/releases/download/v4.5-0.20/perftest-4.5-0.20.gac7cca5.tar.gz
@@ -26,6 +26,9 @@ connections.  It does not work on normal TCP/IP networks, only on
 RDMA networks.
 
 %prep
+# The directory in the tarball has only the part before the dash.
+%global tarball_ver %{lua: uv=rpm.expand("%{upstream_ver}"); d=string.find(uv,"-"); print(string.sub(uv,1,d-1))}
+
 %setup -q -n %{name}-%{tarball_ver}
 find src -type f -iname '*.[ch]' -exec chmod a-x '{}' ';'