diff --git a/ethernet_service.h b/ethernet_service.h
index 3be0a18..4a38958 100644
--- a/ethernet_service.h
+++ b/ethernet_service.h
@@ -31,7 +31,7 @@
   virtual bool TechnologyIs(const Technology::Identifier type) const;
 
   // ethernet_<MAC>
-  virtual std::string GetStorageIdentifier();
+  virtual std::string GetStorageIdentifier() const;
 
  private:
   static const char kServiceType[];