diff --git a/korman/plasma_attributes.py b/korman/plasma_attributes.py
index 9cf651c..478aedf 100644
--- a/korman/plasma_attributes.py
+++ b/korman/plasma_attributes.py
@@ -65,13 +65,17 @@ class PlasmaAttributeVisitor(ast.NodeVisitor):
         return self.generic_visit(node)
 
     def visit_Name(self, node):
-        return(node.id)
+        # Workaround for old Cyan scripts: replace variables named "true" or "false"
+        # with the respective constant values True or False.
+        if node.id.lower() in  {"true", "false"}:
+            return ast.literal_eval(node.id.capitalize())
+        return node.id
 
     def visit_Num(self, node):
-        return(node.n)
+        return node.n
 
     def visit_Str(self, node):
-        return(node.s)
+        return node.s
 
     def visit_List(self, node):
         elts = []
@@ -85,6 +89,9 @@ class PlasmaAttributeVisitor(ast.NodeVisitor):
             elts.append(self.visit(x))
         return tuple(elts)
 
+    def visit_NameConstant(self, node):
+        return node.value
+
     def generic_visit(self, node):
         ast.NodeVisitor.generic_visit(self, node)