diff --git a/cpp/src/phonenumbers/base/synchronization/lock.h b/cpp/src/phonenumbers/base/synchronization/lock.h
index 63eab24c5..296421cd5 100644
--- a/cpp/src/phonenumbers/base/synchronization/lock.h
+++ b/cpp/src/phonenumbers/base/synchronization/lock.h
@@ -44,14 +44,16 @@ namespace phonenumbers {
 
 class Lock {
  public:
-  Lock() : thread_checker_() {}
+  Lock() {}
 
   void Acquire() const {
     DCHECK(thread_checker_.CalledOnValidThread());
+    IGNORE_UNUSED(thread_checker_);
   }
 
   void Release() const {
     DCHECK(thread_checker_.CalledOnValidThread());
+    IGNORE_UNUSED(thread_checker_);
   }
 
  private: