diff --git a/src/Cottle.Test/Parsers/OptimizeParserTester.cs b/src/Cottle.Test/Parsers/OptimizeParserTester.cs
index 0ef43188..484555fd 100644
--- a/src/Cottle.Test/Parsers/OptimizeParserTester.cs
+++ b/src/Cottle.Test/Parsers/OptimizeParserTester.cs
@@ -61,7 +61,7 @@ public void Parse_OptimizeAccess_SkipWhenNonPureIndices()
                     new[]
                     {
                         new ExpressionElement(Expression.CreateConstant(0),
-                            Expression.CreateInvoke(OptimizeParserTester.ImpureFunction, Array.Empty<Expression>())),
+                            Expression.CreateSymbol("AAA")),
                         new ExpressionElement(Expression.CreateConstant(1),
                             Expression.CreateSymbol("BBB")),
                         new ExpressionElement(Expression.CreateSymbol("x"),
diff --git a/src/Cottle/Parsers/Optimize/Optimizers/RecursiveOptimizer.cs b/src/Cottle/Parsers/Optimize/Optimizers/RecursiveOptimizer.cs
index 465f37ef..b1bfb3ca 100644
--- a/src/Cottle/Parsers/Optimize/Optimizers/RecursiveOptimizer.cs
+++ b/src/Cottle/Parsers/Optimize/Optimizers/RecursiveOptimizer.cs
@@ -27,18 +27,18 @@ internal class RecursiveOptimizer : IOptimizer
                         return Expression.CreateConstant(source.Value.Fields[subscript]);
 
                     case ExpressionType.Map:
-                        var impure = false;
+                        var unsure = false;
                         var value = Expression.Void;
 
                         foreach (var element in source.Elements)
                         {
-                            if (!RecursiveOptimizer.IsPure(element.Key) || !RecursiveOptimizer.IsPure(element.Value))
-                                impure = true;
-                            else if (element.Key.Type == ExpressionType.Constant && element.Key.Value == subscript)
+                            if (element.Key.Type != ExpressionType.Constant || !RecursiveOptimizer.IsPure(element.Value))
+                                unsure = true;
+                            else if (element.Key.Value == subscript)
                                 value = element.Value;
                         }
 
-                        return impure ? expression : value;
+                        return unsure ? expression : value;
 
                     default:
                         return expression;