diff --git a/vfs/mem_fs.go b/vfs/mem_fs.go
index bcd799b8c43..62c8e208649 100644
--- a/vfs/mem_fs.go
+++ b/vfs/mem_fs.go
@@ -99,11 +99,11 @@ func (y *MemFS) String() string {
 // SetIgnoreSyncs sets the MemFS.ignoreSyncs field. See the usage comment with NewStrictMem() for
 // details.
 func (y *MemFS) SetIgnoreSyncs(ignoreSyncs bool) {
-	y.mu.Lock()
 	if !y.strict {
 		// noop
 		return
 	}
+	y.mu.Lock()
 	y.ignoreSyncs = ignoreSyncs
 	y.mu.Unlock()
 }