diff --git a/packages/remix-dev/config/flat-routes.ts b/packages/remix-dev/config/flat-routes.ts
index 8b7bb5586e4..27518daada9 100644
--- a/packages/remix-dev/config/flat-routes.ts
+++ b/packages/remix-dev/config/flat-routes.ts
@@ -104,7 +104,7 @@ export function flatRoutes(
 
   let routes: string[] = [];
   for (let entry of entries) {
-    let filepath = path.join(routesDir, entry.name);
+    let filepath = normalizeSlashes(path.join(routesDir, entry.name));
 
     let route: string | null = null;
     // If it's a directory, don't recurse into it, instead just look for a route module
@@ -302,7 +302,7 @@ function findRouteModuleForFile(
   filepath: string,
   ignoredFileRegex: RegExp[]
 ): string | null {
-  let relativePath = path.relative(appDirectory, filepath);
+  let relativePath = normalizeSlashes(path.relative(appDirectory, filepath));
   let isIgnored = ignoredFileRegex.some((regex) => regex.test(relativePath));
   if (isIgnored) return null;
   return filepath;