diff --git a/src/media/store.ts b/src/media/store.ts
index 375499409002..86b2b2ae4150 100644
--- a/src/media/store.ts
+++ b/src/media/store.ts
@@ -84,7 +84,7 @@ function resolveMediaSubdir(subdir: string, caller: string): string {
   if (segments.some((segment) => !segment || segment === "." || segment === "..")) {
     throw new Error(`${caller}: unsafe media subdir: ${JSON.stringify(subdir)}`);
   }
-  return path.join(...segments);
+  return path.posix.join(...segments);
 }
 
 function resolveMediaScopedDir(subdir: string, caller: string): string {
@@ -102,7 +102,7 @@ function resolveMediaRelativePath(id: string, subdir: string, caller: string): s
     throw new Error(`${caller}: unsafe media ID: ${JSON.stringify(id)}`);
   }
   const safeSubdir = resolveMediaSubdir(subdir, caller);
-  return safeSubdir ? path.join(safeSubdir, id) : id;
+  return safeSubdir ? path.posix.join(safeSubdir, id) : id;
 }
 
 function openMediaStore(maxBytes = MAX_BYTES, rootDir = resolveMediaDir()) {