diff --git a/sympde/topology/mapping.py b/sympde/topology/mapping.py
index b7901859..4d5a8720 100644
--- a/sympde/topology/mapping.py
+++ b/sympde/topology/mapping.py
@@ -2,7 +2,7 @@
 
 from collections  import OrderedDict
 
-from sympy import Indexed, IndexedBase, Matrix, ImmutableDenseMatrix
+from sympy import Indexed, IndexedBase, Idx, Matrix, ImmutableDenseMatrix
 from sympy import Function
 from sympy import sympify
 from sympy.core import Basic
@@ -851,6 +851,9 @@ def eval(cls, *_args, **kwargs):
         elif isinstance(expr, Indexed):
             return expr
 
+        elif isinstance(expr, Idx):
+            return expr
+
         elif isinstance(expr, Function):
             return expr