diff --git a/hooks/post-merge b/hooks/post-merge
index 57dcc48..f02614d 100755
--- a/hooks/post-merge
+++ b/hooks/post-merge
@@ -9,7 +9,7 @@
 set -euo pipefail
 
 # Base configuration variables.
-ROOTDIR="$(dirname "$(git rev-parse --git-dir)")"
+ROOTDIR="$(git -C "$(dirname "$0")" rev-parse --show-toplevel)"
 COREOS_CONFIG_DIR="/etc/coreos-home-server"
 SYSTEMD_CONFIG_DIR="/etc/systemd/system"