diff --git a/lib/clientstate-normalizer.ts b/lib/clientstate-normalizer.ts
index 5b44edccb..dec7b5db1 100644
--- a/lib/clientstate-normalizer.ts
+++ b/lib/clientstate-normalizer.ts
@@ -339,7 +339,10 @@ export class ClientStateNormalizer {
                     const session = this.normalized.findSessionById(file.editorId);
                     if (session) {
                         file.content = session.source;
-                        file.filename = session.filename;
+                        if (!file.filename && session.filename) {
+                            // it's fine if the session doesn't contain the filename, the filename in the tree is always leading
+                            file.filename = session.filename;
+                        }
                     }
                 }
             }
diff --git a/lib/handlers/route-api.ts b/lib/handlers/route-api.ts
index b2f7caff4..a1ddb6b7e 100644
--- a/lib/handlers/route-api.ts
+++ b/lib/handlers/route-api.ts
@@ -29,7 +29,7 @@ import express from 'express';
 import {AppDefaultArguments, CompilerExplorerOptions} from '../../app.js';
 import {isString} from '../../shared/common-utils.js';
 import {Language} from '../../types/languages.interfaces.js';
-import {assert, unwrap} from '../assert.js';
+import {assert} from '../assert.js';
 import {ClientStateGoldenifier, ClientStateNormalizer} from '../clientstate-normalizer.js';
 import {ClientState} from '../clientstate.js';
 import {CompilationEnvironment} from '../compilation-env.js';
@@ -281,7 +281,7 @@ export class RouteAPI {
 
                     if (tree.isCMakeProject) {
                         const firstSource = tree.files.find(file => {
-                            return unwrap(file.filename).startsWith('CMakeLists.txt');
+                            return file.filename?.startsWith('CMakeLists.txt');
                         });
 
                         if (firstSource) {
@@ -289,7 +289,7 @@ export class RouteAPI {
                         }
                     } else {
                         const firstSource = tree.files.find(file => {
-                            return unwrap(file.filename).startsWith('example.');
+                            return file.filename?.startsWith('example.');
                         });
 
                         if (firstSource) {