diff --git a/caelus/io/dtypes.py b/caelus/io/dtypes.py
index af03d74..69376cc 100644
--- a/caelus/io/dtypes.py
+++ b/caelus/io/dtypes.py
@@ -234,7 +234,7 @@ def __init__(self, value, semi=True):
         self.value = value
         self.semi = semi
 
-    def write_value(self, fh=sys.stdout, indent_str=''):
+    def write_value(self, fh=sys.stdout, indent_str='', nested=False):
         """Write standalone macro substitution"""
         if self.semi:
             fh.write(indent_str + "%s;\n" % self.value)