diff --git a/src/app/api/chat/conversations/[id]/mark-read/route.js b/src/app/api/chat/conversations/[id]/mark-read/route.js
index aadaccc4..5019386a 100644
--- a/src/app/api/chat/conversations/[id]/mark-read/route.js
+++ b/src/app/api/chat/conversations/[id]/mark-read/route.js
@@ -1,18 +1,24 @@
 import { NextResponse } from 'next/server';
 import { createSupabaseServerClient } from '@/lib/supabase.js';
 
+function normalizeConversationId(conversationId) {
+	return typeof conversationId === 'string' ? conversationId.trim() : '';
+}
+
 /**
  * Mark all messages in a conversation as read for the current user
  * @type {import('./$types').RequestHandler}
  */
 export async function POST(request, { params } = {}) {
 	try {
-		const supabase = await createSupabaseServerClient();
 		const { id: conversationId } = (await params) || {};
+		const normalizedConversationId = normalizeConversationId(conversationId);
 
-		if (!conversationId) {
+		if (!normalizedConversationId) {
 			return NextResponse.json({ error: 'Conversation ID is required' }, { status: 400 });
 		}
+
+		const supabase = await createSupabaseServerClient();
 		
 		// Get user from session
 		const { data: { user }, error: userError } = await supabase.auth.getUser();
@@ -42,7 +48,7 @@ export async function POST(request, { params } = {}) {
 				supabase
 					.from('messages')
 					.select('id')
-					.eq('conversation_id', conversationId)
+					.eq('conversation_id', normalizedConversationId)
 			);
 
 		if (updateError) {
diff --git a/src/app/api/chat/conversations/[id]/mark-read/route.test.js b/src/app/api/chat/conversations/[id]/mark-read/route.test.js
index 9398f70c..1bbae526 100644
--- a/src/app/api/chat/conversations/[id]/mark-read/route.test.js
+++ b/src/app/api/chat/conversations/[id]/mark-read/route.test.js
@@ -1,6 +1,7 @@
 import { beforeEach, describe, expect, it, vi } from 'vitest';
 
 const mocks = vi.hoisted(() => ({
+	createSupabaseServerClient: vi.fn(),
 	authGetUser: vi.fn(),
 	from: vi.fn(),
 	usersEq: vi.fn(),
@@ -9,13 +10,17 @@ const mocks = vi.hoisted(() => ({
 }));
 
 vi.mock('@/lib/supabase.js', () => ({
-	createSupabaseServerClient: vi.fn(async () => ({
+	createSupabaseServerClient: mocks.createSupabaseServerClient
+}));
+
+function createSupabaseClient() {
+	return {
 		auth: {
 			getUser: mocks.authGetUser
 		},
 		from: mocks.from
-	}))
-}));
+	};
+}
 
 function createUsersQuery() {
 	const query = {
@@ -55,6 +60,7 @@ describe('POST /api/chat/conversations/[id]/mark-read', () => {
 		vi.resetModules();
 		vi.clearAllMocks();
 
+		mocks.createSupabaseServerClient.mockResolvedValue(createSupabaseClient());
 		mocks.authGetUser.mockResolvedValue({
 			data: { user: { id: 'auth-user-id' } },
 			error: null
@@ -90,4 +96,17 @@ describe('POST /api/chat/conversations/[id]/mark-read', () => {
 		expect(body).toEqual({ error: 'Conversation ID is required' });
 		expect(mocks.authGetUser).not.toHaveBeenCalled();
 	});
+
+	it('rejects blank conversation ids before creating a Supabase client', async () => {
+		const { POST } = await import('./route.js');
+		const response = await POST(new Request('https://qrypt.chat/api/chat/conversations/%20/mark-read'), {
+			params: Promise.resolve({ id: '   ' })
+		});
+		const body = await response.json();
+
+		expect(response.status).toBe(400);
+		expect(body).toEqual({ error: 'Conversation ID is required' });
+		expect(mocks.createSupabaseServerClient).not.toHaveBeenCalled();
+		expect(mocks.authGetUser).not.toHaveBeenCalled();
+	});
 });