diff --git a/frontend/src/hooks/documents/useDocumentCorrespondentActions.ts b/frontend/src/hooks/documents/useDocumentCorrespondentActions.ts
index 28ba59c..65c57a4 100644
--- a/frontend/src/hooks/documents/useDocumentCorrespondentActions.ts
+++ b/frontend/src/hooks/documents/useDocumentCorrespondentActions.ts
@@ -1,5 +1,5 @@
 import { useCallback, useMemo } from 'react';
-import { isPlainObject, isStringValue } from '../../utils/typeGuards';
+import { isPlainObject } from '../../utils/typeGuards';
 
 type ApiClient = {
   post: (path: string, body?: unknown) => Promise<{ data: unknown }>;
@@ -127,7 +127,7 @@ const useDocumentCorrespondentActions = ({
     if (isPlainObject(option) && 'id' in option) {
       return option as CorrespondentOption;
     }
-    if (isStringValue(option)) {
+    if (typeof option === 'string') {
       const trimmed = option.trim();
       if (trimmed) {
         return { id: null, name: trimmed };
diff --git a/frontend/src/utils/typeGuards.ts b/frontend/src/utils/typeGuards.ts
index ca9260f..40d70a5 100644
--- a/frontend/src/utils/typeGuards.ts
+++ b/frontend/src/utils/typeGuards.ts
@@ -3,5 +3,4 @@ const objectToString = Object.prototype.toString;
 export const isPlainObject = (value: unknown): value is Record<string, unknown> =>
   value !== null && !Array.isArray(value) && Object(value) === value;
 
-export const isStringValue = (value: unknown): value is string =>
-  objectToString.call(value) === '[object String]';
+
diff --git a/frontend/src/utils/webauthn.ts b/frontend/src/utils/webauthn.ts
index 555cff8..f2aba51 100644
--- a/frontend/src/utils/webauthn.ts
+++ b/frontend/src/utils/webauthn.ts
@@ -26,8 +26,6 @@ type AuthenticationCredential = PublicKeyCredential & {
   response: AuthenticatorAssertionResponse;
 };
 
-import { isStringValue } from './typeGuards';
-
 const base64urlToBase64 = (value: string = ''): string => {
   const normalized = value.replace(/-/g, '+').replace(/_/g, '/');
   const padding = normalized.length % 4;
@@ -103,14 +101,14 @@ export const preparePublicKeyCreationOptions = (
 
   const publicKey: PublicKeyCredentialCreationOptions = { ...challengeResponse.publicKey };
 
-  if (publicKey.challenge && isStringValue(publicKey.challenge)) {
+  if (publicKey.challenge && typeof publicKey.challenge === 'string') {
     publicKey.challenge = base64urlToBufferSource(publicKey.challenge);
   }
 
   if (publicKey.user?.id) {
     publicKey.user = {
       ...publicKey.user,
-      id: isStringValue(publicKey.user.id)
+      id: typeof publicKey.user.id === 'string'
         ? base64urlToBufferSource(publicKey.user.id)
         : publicKey.user.id,
     };
@@ -119,7 +117,7 @@ export const preparePublicKeyCreationOptions = (
   if (Array.isArray(publicKey.excludeCredentials)) {
     publicKey.excludeCredentials = publicKey.excludeCredentials.map((descriptor) => ({
       ...descriptor,
-      id: isStringValue(descriptor.id)
+      id: typeof descriptor.id === 'string'
         ? base64urlToBufferSource(descriptor.id)
         : descriptor.id,
     }));
@@ -141,14 +139,14 @@ export const preparePublicKeyRequestOptions = (
 
   const publicKey: PublicKeyCredentialRequestOptions = { ...challengeResponse.publicKey };
 
-  if (publicKey.challenge && isStringValue(publicKey.challenge)) {
+  if (publicKey.challenge && typeof publicKey.challenge === 'string') {
     publicKey.challenge = base64urlToBufferSource(publicKey.challenge);
   }
 
   if (Array.isArray(publicKey.allowCredentials)) {
     publicKey.allowCredentials = publicKey.allowCredentials.map((descriptor) => ({
       ...descriptor,
-      id: isStringValue(descriptor.id)
+      id: typeof descriptor.id === 'string'
         ? base64urlToBufferSource(descriptor.id)
         : descriptor.id,
     }));