diff --git a/src/utils.tsx b/src/utils.tsx
index d26a256c..94a2536e 100644
--- a/src/utils.tsx
+++ b/src/utils.tsx
@@ -4,6 +4,15 @@ const CODE_RE = /[?&]code=[^&]+/;
 const STATE_RE = /[?&]state=[^&]+/;
 const ERROR_RE = /[?&]error=[^&]+/;
 
+interface WithError {
+  error: string;
+}
+
+interface WithErrorAndDescription {
+  error: string;
+  error_description: string;
+}
+
 export const hasAuthParams = (searchParams = window.location.search): boolean =>
   (CODE_RE.test(searchParams) || ERROR_RE.test(searchParams)) &&
   STATE_RE.test(searchParams);
@@ -19,15 +28,17 @@ const normalizeErrorFn =
       error !== null &&
       typeof error === 'object' &&
       'error' in error &&
-      typeof error.error === 'string'
+      typeof (error as WithError).error === 'string'
     ) {
       if (
         'error_description' in error &&
-        typeof error.error_description === 'string'
+        typeof (error as WithErrorAndDescription).error_description === 'string'
       ) {
-        return new OAuthError(error.error, error.error_description);
+        const e = error as WithErrorAndDescription;
+        return new OAuthError(e.error, e.error_description);
       }
-      return new OAuthError(error.error);
+      const e = error as WithError;
+      return new OAuthError(e.error);
     }
     return new Error(fallbackMessage);
   };