diff --git a/transport/include/hidl/HidlTransportSupport.h b/transport/include/hidl/HidlTransportSupport.h
index 8476f47..8a2a70a 100644
--- a/transport/include/hidl/HidlTransportSupport.h
+++ b/transport/include/hidl/HidlTransportSupport.h
@@ -47,6 +47,8 @@
  */
 void joinRpcThreadpool();
 
+namespace details {
+
 // cast the interface IParent to IChild.
 // Return nullptr if parent is null or any failure.
 template<typename IChild, typename IParent, typename BpChild, typename BpParent>
@@ -69,6 +71,8 @@
     return sp<IChild>(static_cast<IChild *>(parent.get()));
 }
 
+}  // namespace details
+
 }  // namespace hardware
 }  // namespace android