diff --git a/pymath/expression.py b/pymath/expression.py
index 4ec22ea..0e7038b 100644
--- a/pymath/expression.py
+++ b/pymath/expression.py
@@ -89,7 +89,8 @@ class Expression(Explicable):
         if type(exp) == str:
             expression.postfix_tokens = str2tokens(exp) 
         elif type(exp) == list:
-            expression.postfix_tokens = flatten_list([tok.postfix_tokens if Expression.isExpression(tok) else tok for tok in exp])
+            exp_mod_op = [op.get_op(i) if (str(i) in "+-*/^" and not isOperator(i)) else i for i in exp]
+            expression.postfix_tokens = flatten_list([tok.postfix_tokens if Expression.isExpression(tok) else tok for tok in exp_mod_op])
         elif type(exp) == Expression:
             return exp 
         else: