diff --git a/api/package.json b/api/package.json
index 6a43d32a49f..5851c428337 100644
--- a/api/package.json
+++ b/api/package.json
@@ -6,7 +6,7 @@
   "dependencies": {
     "@aws-sdk/client-ses": "3.521.0",
     "@fastify/accepts": "4.3.0",
-    "@fastify/cookie": "9.3.1",
+    "@fastify/cookie": "9.4.0",
     "@fastify/csrf-protection": "6.4.1",
     "@fastify/express": "^2.3.0",
     "@fastify/swagger": "8.14.0",
diff --git a/api/src/plugins/code-flow-auth.ts b/api/src/plugins/code-flow-auth.ts
index b76594ab261..7b9e8cca6eb 100644
--- a/api/src/plugins/code-flow-auth.ts
+++ b/api/src/plugins/code-flow-auth.ts
@@ -78,12 +78,12 @@ const codeFlowAuth: FastifyPluginCallback = (fastify, _options, done) => {
       const jwtAccessToken = unsignedToken.value;
 
       try {
-        jwt.verify(jwtAccessToken!, JWT_SECRET);
+        jwt.verify(jwtAccessToken, JWT_SECRET);
       } catch {
         return rejectStrategy(req, reply, TOKEN_INVALID);
       }
 
-      const { accessToken } = jwt.decode(jwtAccessToken!) as {
+      const { accessToken } = jwt.decode(jwtAccessToken) as {
         accessToken: Token;
       };
 
diff --git a/api/src/plugins/cookies.ts b/api/src/plugins/cookies.ts
index 795b2b683f1..2161aec8515 100644
--- a/api/src/plugins/cookies.ts
+++ b/api/src/plugins/cookies.ts
@@ -1,4 +1,4 @@
-import fastifyCookie from '@fastify/cookie';
+import fastifyCookie, { type UnsignResult } from '@fastify/cookie';
 import { FastifyPluginCallback } from 'fastify';
 import fp from 'fastify-plugin';
 
@@ -23,7 +23,7 @@ export const sign = (value: string) =>
  * @param rawValue The signed cookie value.
  * @returns The unsigned cookie value.
  */
-export const unsign = (rawValue: string) => {
+export const unsign = (rawValue: string): UnsignResult => {
   const prefix = rawValue.slice(0, 2);
   if (prefix !== 's:') return { valid: false, renew: false, value: null };
 
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 05564135d52..23ac84489a4 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -157,8 +157,8 @@ importers:
         specifier: 4.3.0
         version: 4.3.0
       '@fastify/cookie':
-        specifier: 9.3.1
-        version: 9.3.1
+        specifier: 9.4.0
+        version: 9.4.0
       '@fastify/csrf-protection':
         specifier: 6.4.1
         version: 6.4.1
@@ -2971,8 +2971,8 @@ packages:
   '@fastify/ajv-compiler@3.5.0':
     resolution: {integrity: sha512-ebbEtlI7dxXF5ziNdr05mOY8NnDiPB1XvAlLHctRt/Rc+C3LCOVW5imUVX+mhvUhnNzmPBHewUkOFgGlCxgdAA==}
 
-  '@fastify/cookie@9.3.1':
-    resolution: {integrity: sha512-h1NAEhB266+ZbZ0e9qUE6NnNR07i7DnNXWG9VbbZ8uC6O/hxHpl+Zoe5sw1yfdZ2U6XhToUGDnzQtWJdCaPwfg==}
+  '@fastify/cookie@9.4.0':
+    resolution: {integrity: sha512-Th+pt3kEkh4MQD/Q2q1bMuJIB5NX/D5SwSpOKu3G/tjoGbwfpurIMJsWSPS0SJJ4eyjtmQ8OipDQspf8RbUOlg==}
 
   '@fastify/csrf-protection@6.4.1':
     resolution: {integrity: sha512-nP1xjruddvWMvqjxTVzpLqWVLAX7P/XWkeTaARg3bXVrVmpDWjDMN7KfV3swIT/XexjDooMo+QG/n0n6ynZaiw==}
@@ -17095,7 +17095,7 @@ snapshots:
       ajv-formats: 2.1.1(ajv@8.12.0)
       fast-uri: 2.3.0
 
-  '@fastify/cookie@9.3.1':
+  '@fastify/cookie@9.4.0':
     dependencies:
       cookie-signature: 1.2.1
       fastify-plugin: 4.5.1