diff --git a/src/__tests__/types.test.ts b/src/__tests__/types.test.ts
index 85b20776e..1926ce634 100644
--- a/src/__tests__/types.test.ts
+++ b/src/__tests__/types.test.ts
@@ -166,12 +166,23 @@ describe('types', () => {
         });
       });
 
-      test('options', () => {
-        types.number({
+      test('options, range and modulo', () => {
+        const options = {
           maximum: 9,
           minimum: 2,
           multipleOf: 2,
-        });
+        } as const;
+        types.number(options);
+
+        // @ts-expect-error invalid option
+        types.number({ maxLength: 1 });
+      });
+
+      test('options, enum', () => {
+        const options = {
+          enum: [1, 2, 3],
+        } as const;
+        types.number(options);
 
         // @ts-expect-error invalid option
         types.number({ maxLength: 1 });
@@ -327,11 +338,12 @@ describe('types', () => {
       });
 
       test('options', () => {
-        types.string({
+        const options = {
           enum: ['foo', 'bar'],
           maxLength: 9,
           minLength: 1,
-        });
+        } as const;
+        types.string(options);
 
         // @ts-expect-error invalid option
         types.string({ maximum: 1 });
diff --git a/src/types.ts b/src/types.ts
index 7a98543a4..0a36e616a 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -18,7 +18,7 @@ interface ArrayOptions extends GenericOptions {
 }
 
 interface NumberOptions extends GenericOptions {
-  enum?: number[];
+  enum?: readonly number[];
   exclusiveMaximum?: boolean;
   exclusiveMinimum?: boolean;
   maximum?: number;
@@ -35,7 +35,7 @@ interface ObjectOptions extends GenericOptions {
 }
 
 interface StringOptions extends GenericOptions {
-  enum?: string[];
+  enum?: readonly string[];
   maxLength?: number;
   minLength?: number;
   pattern?: string;