diff --git a/scripts/install b/scripts/install
index b36fb31..b3c27f7 100755
--- a/scripts/install
+++ b/scripts/install
@@ -28,7 +28,7 @@ source_id="main"
 if [ "$version_to_follow" == "oldstable" ]; then
     last_version=$(ynh_read_manifest --manifest_key="resources.sources.main.url" | grep -o '[0-9][0-9]\.[0-9]\.[0-9]')
     last_major_version=${last_version%%.*}
-    source_id=$((last_major_version--))
+    last_major_version=$(( $last_major_version - 1 ))
 fi
 # Download, check integrity, uncompress and patch the source from app.src
 ynh_setup_source --dest_dir="$install_dir" --source_id="$source_id"