diff --git a/src/evaluator/expression/prefix/mod.rs b/src/evaluator/expression/prefix/mod.rs
index 7ed148d7..869f61a2 100644
--- a/src/evaluator/expression/prefix/mod.rs
+++ b/src/evaluator/expression/prefix/mod.rs
@@ -13,7 +13,7 @@ impl Evaluator {
         match object {
             Object::True => Ok(Object::False),
             Object::False => Ok(Object::True),
-            _ => Err(EvaluationError::UnknownOperator),
+            _ => Err(EvaluationError::TypeMismatch),
         }
     }
 
diff --git a/src/tests/evaluation_error/type_mismatch_integer_prefix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_integer_prefix_expression__test_type_mismatch_integer_prefix_expression_case_1_evaluation_error.snap b/src/tests/evaluation_error/type_mismatch_integer_prefix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_integer_prefix_expression__test_type_mismatch_integer_prefix_expression_case_1_evaluation_error.snap
index 1e66604e..d39949af 100644
--- a/src/tests/evaluation_error/type_mismatch_integer_prefix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_integer_prefix_expression__test_type_mismatch_integer_prefix_expression_case_1_evaluation_error.snap
+++ b/src/tests/evaluation_error/type_mismatch_integer_prefix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_integer_prefix_expression__test_type_mismatch_integer_prefix_expression_case_1_evaluation_error.snap
@@ -3,5 +3,5 @@ source: src/tests/evaluation_error/type_mismatch_integer_prefix_expression/mod.r
 expression: error
 ---
 Err(
-    UnknownOperator,
+    TypeMismatch,
 )