diff --git a/library/src/methods/flatten/flatten.test-d.ts b/library/src/methods/flatten/flatten.test-d.ts
index 848e0358b..b2b7b6d29 100644
--- a/library/src/methods/flatten/flatten.test-d.ts
+++ b/library/src/methods/flatten/flatten.test-d.ts
@@ -80,4 +80,15 @@ describe('flatten', () => {
       readonly other?: [string, ...string[]];
     }>();
   });
+
+  test('should accept readonly list of errors', () => {
+    const readonlyIssues = issues as Readonly<typeof issues>;
+    expectTypeOf(flatten(readonlyIssues)).toEqualTypeOf<{
+      readonly root?: [string, ...string[]];
+      readonly nested?: Readonly<
+        Partial<Record<string, [string, ...string[]]>>
+      >;
+      readonly other?: [string, ...string[]];
+    }>();
+  });
 });
diff --git a/library/src/methods/flatten/flatten.ts b/library/src/methods/flatten/flatten.ts
index 891753145..1dad5a61d 100644
--- a/library/src/methods/flatten/flatten.ts
+++ b/library/src/methods/flatten/flatten.ts
@@ -63,7 +63,7 @@ export type FlatErrors<
  * @returns A flat error object.
  */
 export function flatten(
-  issues: [BaseIssue<unknown>, ...BaseIssue<unknown>[]]
+  issues: readonly [BaseIssue<unknown>, ...BaseIssue<unknown>[]]
 ): FlatErrors<undefined>;
 
 /**
@@ -77,11 +77,11 @@ export function flatten<
   TSchema extends
     | BaseSchema<unknown, unknown, BaseIssue<unknown>>
     | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
->(issues: [InferIssue<TSchema>, ...InferIssue<TSchema>[]]): FlatErrors<TSchema>;
+>(issues: readonly [InferIssue<TSchema>, ...InferIssue<TSchema>[]]): FlatErrors<TSchema>;
 
 // @__NO_SIDE_EFFECTS__
 export function flatten(
-  issues: [BaseIssue<unknown>, ...BaseIssue<unknown>[]]
+  issues: readonly [BaseIssue<unknown>, ...BaseIssue<unknown>[]]
 ): FlatErrors<undefined> {
   // Create flat errors object
   const flatErrors: FlatErrors<undefined> = {};