diff --git a/src/vfs/resolver.go b/src/vfs/resolver.go
index 481dc92..3c697b6 100644
--- a/src/vfs/resolver.go
+++ b/src/vfs/resolver.go
@@ -235,6 +235,9 @@ func (r *Resolver) nestedFs(ctx context.Context, fsPath string, file File) (File
 		return nil, fmt.Errorf("error calculating file hash: %w", err)
 	}
 
+	r.m.Lock()
+	defer r.m.Unlock()
+
 	if nestedFs, ok := r.fsmap[fileHash]; ok {
 		return nestedFs, file.Close(ctx)
 	}