diff --git a/compose.smtp.yml b/compose.smtp.yml
index 293dd20..134fffe 100644
--- a/compose.smtp.yml
+++ b/compose.smtp.yml
@@ -7,7 +7,7 @@ services:
       - smtp_password
     environment:
       - SMTP_HOST=${SMTP_HOST}
-      - SMTP_PORT=${SMTP_PORT:25}
+      - SMTP_PORT=${SMTP_PORT:-25}
       - SMTP_AUTH=${SMTP_AUTH}
       - SMTP_TLS=${SMTP_TLS}
       - MAIL_FROM=${MAIL_FROM}