diff --git a/transformations.py b/transformations.py
index e2c2e22919f12cf98727263c1c1fb2ac74a8bf61..565367b9af5420433c7f28458e7a028b3b0ce026 100644
--- a/transformations.py
+++ b/transformations.py
@@ -15,6 +15,8 @@ def fastSubs(term, subsDict):
     def visit(expr):
         if expr in subsDict:
             return subsDict[expr]
+        if not hasattr(expr, 'args'):
+            return expr
         paramList = [visit(a) for a in expr.args]
         return expr if not paramList else expr.func(*paramList)
     return visit(term)