diff --git a/manage-server/install.sh b/manage-server/install.sh
index 7f66d9e..b954695 100755
--- a/manage-server/install.sh
+++ b/manage-server/install.sh
@@ -14,7 +14,7 @@
 #   --no-tls                        Skip the TLS-required sanity check (dev).
 set -euo pipefail
 
-SCRIPT_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" &>/dev/null && pwd)"
+SCRIPT_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]:-$0}")" &>/dev/null && pwd)"
 cd "$SCRIPT_DIR"
 
 info() { printf '[manage-server] %s\n' "$*"; }
diff --git a/manage-server/uninstall.sh b/manage-server/uninstall.sh
index 52d87af..a6fcd9a 100755
--- a/manage-server/uninstall.sh
+++ b/manage-server/uninstall.sh
@@ -9,7 +9,7 @@
 #   sudo bash uninstall.sh --purge-data  # also delete DB + binaries volume
 set -euo pipefail
 
-SCRIPT_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" &>/dev/null && pwd)"
+SCRIPT_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]:-$0}")" &>/dev/null && pwd)"
 cd "$SCRIPT_DIR"
 
 info() { printf '[manage-server] %s\n' "$*"; }
diff --git a/manage-server/upgrade.sh b/manage-server/upgrade.sh
index fae755a..d4c19e7 100755
--- a/manage-server/upgrade.sh
+++ b/manage-server/upgrade.sh
@@ -9,7 +9,7 @@
 #   sudo bash upgrade.sh --image TAG    # pin a specific image tag
 set -euo pipefail
 
-SCRIPT_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" &>/dev/null && pwd)"
+SCRIPT_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]:-$0}")" &>/dev/null && pwd)"
 cd "$SCRIPT_DIR"
 
 info() { printf '[manage-server] %s\n' "$*"; }