diff --git a/libraries/chain/include/graphene/chain/protocol/types.hpp b/libraries/chain/include/graphene/chain/protocol/types.hpp
index 6fa2ab4d..3c5b4e33 100644
--- a/libraries/chain/include/graphene/chain/protocol/types.hpp
+++ b/libraries/chain/include/graphene/chain/protocol/types.hpp
@@ -355,6 +355,7 @@ namespace graphene { namespace chain {
        friend bool operator == ( const public_key_type& p1, const fc::ecc::public_key& p2);
        friend bool operator == ( const public_key_type& p1, const public_key_type& p2);
        friend bool operator != ( const public_key_type& p1, const public_key_type& p2);
+       friend bool operator < ( const public_key_type& p1, const public_key_type& p2);
        // TODO: This is temporary for testing
        bool is_valid_v1( const std::string& base58str );
        bool is_valid_muse( const std::string& base58str );
diff --git a/libraries/chain/protocol/types.cpp b/libraries/chain/protocol/types.cpp
index b7cac207..0dd753fb 100644
--- a/libraries/chain/protocol/types.cpp
+++ b/libraries/chain/protocol/types.cpp
@@ -134,7 +134,12 @@ namespace graphene { namespace chain {
     {
        return p1.key_data != p2.key_data;
     }
-    
+
+    bool operator < ( const public_key_type& p1, const public_key_type& p2)
+    {
+       return p1.key_data < p2.key_data;
+    }
+
     // extended_public_key_type
     
     extended_public_key_type::extended_public_key_type():key_data(){};