diff --git a/scripts/first-boot-containers.sh b/scripts/first-boot-containers.sh
index b020a5d7..2aeab34e 100644
--- a/scripts/first-boot-containers.sh
+++ b/scripts/first-boot-containers.sh
@@ -836,6 +836,21 @@ fi
 
 # 9. Custom UI containers (bitcoin-ui, lnd-ui)
 # These are built from Dockerfiles in /opt/archipelago/docker/ or loaded from pre-built images.
+
+# Inject Bitcoin RPC auth into bitcoin-ui nginx.conf BEFORE building
+RPC_USER="archipelago"
+RPC_PASS_FILE="/var/lib/archipelago/secrets/bitcoin-rpc-password"
+if [ -f "$RPC_PASS_FILE" ]; then
+  RPC_PASS=$(cat "$RPC_PASS_FILE")
+  AUTH_B64=$(echo -n "${RPC_USER}:${RPC_PASS}" | base64)
+  for ui_dir in /opt/archipelago/docker/bitcoin-ui /home/archipelago/archy/docker/bitcoin-ui; do
+    if [ -f "$ui_dir/nginx.conf" ]; then
+      sed -i "s|__BITCOIN_RPC_AUTH__|${AUTH_B64}|g" "$ui_dir/nginx.conf"
+      log "Injected Bitcoin RPC auth into $ui_dir/nginx.conf"
+    fi
+  done
+fi
+
 for ui in bitcoin-ui lnd-ui; do
   if $DOCKER ps --format '{{.Names}}' 2>/dev/null | grep -q "$ui"; then
     continue