diff --git a/hooks/pre-commit b/hooks/pre-commit
index 7862b68..dc0f8ae 100755
--- a/hooks/pre-commit
+++ b/hooks/pre-commit
@@ -4,7 +4,9 @@ set -eu
 
 # make the GIT_DIR and GIT_INDEX_FILE absolute, before we change dir
 export GIT_DIR=$(readlink -f `git rev-parse --git-dir`)
-export GIT_INDEX_FILE=$(readlink -f `git rev-parse --git-path index`)
+if [ -n "$GIT_INDEX_FILE" ]; then
+    export GIT_INDEX_FILE=$(readlink -f "$GIT_INDEX_FILE")
+fi
 
 wd=`pwd`