diff --git a/src/z3c/rml/special.py b/src/z3c/rml/special.py
index 67dda39..7fda8d0 100644
--- a/src/z3c/rml/special.py
+++ b/src/z3c/rml/special.py
@@ -79,7 +79,7 @@ def getName(self, elem, canvas):
         )
 
     def evalString(self, elem, canvas):
-        return do_eval(self._getText(elem, canvas))
+        return do_eval(self._getText(elem, canvas, False))
 
     def namedString(self, elem, canvas):
         self._getManager().names[elem.get('id')] = self._getText(