diff --git a/docker-compose.yml b/docker-compose.yml
index 232b814..6f44302 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -107,6 +107,11 @@ services:
     image: boltz/bitcoin-core:25.0
     command:
       - -regtest
+      # creds for the lnbits regtest test harness (tests/regtest/helpers.py uses
+      # -rpcuser=lnbits -rpcpassword=lnbits). rpcauth keeps the auto-generated
+      # cookie working too, so the LN nodes' --bitcoind.rpccookie auth is intact.
+      # $$ escapes compose interpolation. (user=lnbits, password=lnbits)
+      - -rpcauth=lnbits:a1b2c3d4e5f60718293a4b5c6d7e8f90$$64c29b7500c0e20b7917aa7f6dc6ce3eec896dd8f0bd3834f98c5ee489ef233f
       - -fallbackfee=0.00000253
       - -zmqpubrawtx=tcp://0.0.0.0:29000
       - -zmqpubrawblock=tcp://0.0.0.0:29001