diff --git a/schala-lang/language/src/eval.rs b/schala-lang/language/src/eval.rs
index d78ab62..7fcd636 100644
--- a/schala-lang/language/src/eval.rs
+++ b/schala-lang/language/src/eval.rs
@@ -529,6 +529,12 @@ mod eval_tests {
     */
   }
 
+  #[test]
+  fn op_eval() {
+    test_in_fresh_env!("- 13", "-13");
+    test_in_fresh_env!("10 - 2", "8");
+  }
+
   #[test]
   fn function_eval() {
     test_in_fresh_env!("fn oi(x) { x + 1 }; oi(4)", "5");
diff --git a/schala-lang/language/src/reduced_ast.rs b/schala-lang/language/src/reduced_ast.rs
index e90a056..8b52bbf 100644
--- a/schala-lang/language/src/reduced_ast.rs
+++ b/schala-lang/language/src/reduced_ast.rs
@@ -450,7 +450,7 @@ impl BinOp {
 
 impl PrefixOp {
   fn reduce(&self, symbol_table: &SymbolTable, arg: &Box<Meta<Expression>>) -> Expr {
-    match Builtin::from_str(self.sigil()).ok() {
+    match self.builtin {
       Some(op) => {
         let f = Box::new(Expr::Func(Func::BuiltIn(op)));
         Expr::Call { f, args: vec![arg.node().reduce(symbol_table)]}