diff --git a/src/authentic2/utils/evaluate.py b/src/authentic2/utils/evaluate.py
index a79577702..90474f3ef 100644
--- a/src/authentic2/utils/evaluate.py
+++ b/src/authentic2/utils/evaluate.py
@@ -91,7 +91,7 @@ class BaseExpressionValidator(ast.NodeVisitor):
         else:
             ok = True
         if not ok:
-            raise ExpressionError(_('expression is forbidden'), node=node, code='forbidden-expression')
+            raise ExpressionError(_('expression "%(expression)s" is forbidden'), node=node, code='forbidden-expression')
 
         # specific node class check
         node_name = node.__class__.__name__
@@ -123,6 +123,7 @@ class BaseExpressionValidator(ast.NodeVisitor):
         except ExpressionError as e:
             if e.text is None:
                 e.text = expression
+            e.params = {'expression': expression}
             six.reraise(*sys.exc_info())
         return compile(tree, expression, mode='eval')
 
diff --git a/tests/test_utils_evaluate.py b/tests/test_utils_evaluate.py
index e6d1bbb48..69a217952 100644
--- a/tests/test_utils_evaluate.py
+++ b/tests/test_utils_evaluate.py
@@ -53,6 +53,7 @@ def test_condition_validator():
 
     with pytest.raises(ExpressionError) as raised:
         v('a + b')
+    assert str(raised.value) == '[\'expression "a + b" is forbidden\']'
 
     with pytest.raises(ExpressionError) as raised:
         v('1 + 2')