diff --git a/ct/debian.sh b/ct/debian.sh
index 4ddf25c122..eb443ec20a 100644
--- a/ct/debian.sh
+++ b/ct/debian.sh
@@ -1,5 +1,9 @@
 #!/usr/bin/env bash
-source "$(dirname "${BASH_SOURCE[0]}")/../misc/build.func" 2>/dev/null || source <(curl -fsSL "${COMMUNITY_SCRIPTS_URL:-https://raw.githubusercontent.com/community-scripts/ProxmoxVED/main}/misc/build.func")
+# Engine comes from community-scripts/core; this repo only ships the scripts.
+# Local checkout wins (COMMUNITY_SCRIPTS_CORE_DIR, else a sibling ../core), so a
+# fork/branch of core can be tested without touching this file.
+_cs_boot="${COMMUNITY_SCRIPTS_CORE_DIR:-$(dirname "${BASH_SOURCE[0]}")/../../core}/shared/build.func"
+source "$_cs_boot" 2>/dev/null || source <(curl -fsSL "${COMMUNITY_SCRIPTS_CORE_URL:-https://raw.githubusercontent.com/community-scripts/core/main}/shared/build.func")
 
 # Copyright (c) 2021-2026 community-scripts ORG
 # Author: MickLesk (CanbiZ)