diff --git a/.env.example b/.env.example
index 3c5716c..4f304e1 100644
--- a/.env.example
+++ b/.env.example
@@ -1,5 +1,7 @@
 NET_ID=42
 RPC_URL=https://kovan.infura.io
+
+# without 0x prefix
 PRIVATE_KEY=
 # 2.5 means 2.5%
 RELAYER_FEE=2.5
diff --git a/README.md b/README.md
index 1650949..fa3b518 100644
--- a/README.md
+++ b/README.md
@@ -20,7 +20,7 @@ docker-compose.yml contains a stack that will automatically provision SSL certif
 
 1. Download docker-compose.yml
 2. Change environment variables for `kovan` containers as appropriate
-    * add `PRIVATE_KEY` for your relayer address
+    * add `PRIVATE_KEY` for your relayer address (without 0x prefix)
     * set `VIRTUAL_HOST` and `LETSENCRYPT_HOST` to your domain and add DNS record pointing to your relayer ip address
     * customize `RELAYER_FEE`
     * update `RPC_URL` if needed
diff --git a/docker-compose.yml b/docker-compose.yml
index 7b0e333..153e851 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -8,6 +8,7 @@ services:
       LETSENCRYPT_HOST: example.duckdns.org
       NET_ID: 42
       RPC_URL: https://kovan.infura.io
+      # without 0x prefix
       PRIVATE_KEY:
       # 2.5 means 2.5%
       RELAYER_FEE: 2.5