diff --git a/net/fill_config.py b/net/fill_config.py
index b7fa142..d68f50c 100755
--- a/net/fill_config.py
+++ b/net/fill_config.py
@@ -89,7 +89,7 @@ for line in open(local_config_file):
   local_config[name] = val
 
 # replace variable names with above values recursively
-replace_re = re.compile('\$\{([A-Z][A-Za-z0-9_]*)\}')
+replace_re = re.compile('\$\{([A-Z_][A-Za-z0-9_]*)\}')
 command_re = re.compile('\$\{([a-z][A-Za-z0-9_]*)\(([^)]*)\)\}')
 
 idx = 0