diff --git a/gn.spec b/gn.spec
index d0f3f36..877c95b 100644
--- a/gn.spec
+++ b/gn.spec
@@ -26,7 +26,7 @@ Name:           gn
 # See https://gn.googlesource.com/gn/+log for the latest changes.
 %global commit 88e8054aff7bd0cb2295c7d9361d2be0b7355f27
 %global access 20240301
-%global shortcommit %{sub %{commit} 1 12}
+%global shortcommit %(c='%{commit}'; echo "${c:0:12}")
 %global position 2154
 Version:        %{position}^%{access}git%{shortcommit}
 Release:        %autorelease