diff --git a/docker/local.env.sample.development b/docker/local.env.sample.development
index db1caed784..b26ed112f2 100644
--- a/docker/local.env.sample.development
+++ b/docker/local.env.sample.development
@@ -1,6 +1,8 @@
 USE_LETS_ENCRYPT=false
 PRIMERO_HOST=localhost
 PRIMERO_SECRET_KEY_BASE=PRIMERO_SECRET_KEY_BASE
+# PRIMERO_MESSAGE_SECRET must be exactly 32 bytes.
+PRIMERO_MESSAGE_SECRET=secret-key-message-primero-12345
 POSTGRES_PASSWORD=primero
 POSTGRES_DB=primero_development
 DEVISE_SECRET_KEY=DEVISE_SECRET_KEY