diff --git a/base/include/hidl/HidlSupport.h b/base/include/hidl/HidlSupport.h
index 8d43bfd..e201a1e 100644
--- a/base/include/hidl/HidlSupport.h
+++ b/base/include/hidl/HidlSupport.h
@@ -154,6 +154,8 @@
     // to maintain this hidl_string alive.
     operator const char *() const;
 
+    bool operator< (const hidl_string &rhs) const;
+
     void clear();
 
     // Reference an external char array. Ownership is _not_ transferred.