diff --git a/onionmaker/__main__.py b/onionmaker/__main__.py
index 968092e..c5a857f 100644
--- a/onionmaker/__main__.py
+++ b/onionmaker/__main__.py
@@ -22,7 +22,7 @@
 PUBLIC_KEY_FILENAME = 'hs_ed25519_public_key'
 PRIVATE_KEY_FILENAME = 'hs_ed25519_secret_key'
 
-RANDOM_VALUE_REGEX = re.compile(r'^[a-z0-9]{32}$', re.IGNORECASE)
+RANDOM_VALUE_REGEX = re.compile(r'^[a-z0-9_]{32}$', re.IGNORECASE)
 
 
 def _validate_random_value(value):