diff --git a/src/mechanism.cpp b/src/mechanism.cpp
index 42d2b67b..6c6f265b 100644
--- a/src/mechanism.cpp
+++ b/src/mechanism.cpp
@@ -63,7 +63,7 @@ void zmq::mechanism_t::peer_routing_id (msg_t *msg_)
 void zmq::mechanism_t::set_user_id (const void *data_, size_t size_)
 {
     _user_id.set (static_cast<const unsigned char *> (data_), size_);
-    zap_properties.ZMQ_MAP_INSERT_OR_EMPLACE (
+    _zap_properties.ZMQ_MAP_INSERT_OR_EMPLACE (
       std::string (ZMQ_MSG_PROPERTY_USER_ID),
       std::string (reinterpret_cast<const char *> (data_), size_));
 }
@@ -268,7 +268,7 @@ int zmq::mechanism_t::parse_metadata (const unsigned char *ptr_,
             if (rc == -1)
                 return -1;
         }
-        (zap_flag_ ? zap_properties : zmtp_properties)
+        (zap_flag_ ? _zap_properties : _zmtp_properties)
           .ZMQ_MAP_INSERT_OR_EMPLACE (
             name,
             std::string (reinterpret_cast<const char *> (value), value_length));
diff --git a/src/mechanism.hpp b/src/mechanism.hpp
index b96a9d8e..edd58a8f 100644
--- a/src/mechanism.hpp
+++ b/src/mechanism.hpp
@@ -81,9 +81,12 @@ class mechanism_t
 
     const blob_t &get_user_id () const;
 
-    const metadata_t::dict_t &get_zmtp_properties () { return zmtp_properties; }
+    const metadata_t::dict_t &get_zmtp_properties ()
+    {
+        return _zmtp_properties;
+    }
 
-    const metadata_t::dict_t &get_zap_properties () { return zap_properties; }
+    const metadata_t::dict_t &get_zap_properties () { return _zap_properties; }
 
   protected:
     //  Only used to identify the socket for the Socket-Type
@@ -123,15 +126,15 @@ class mechanism_t
     virtual int
     property (const std::string &name_, const void *value_, size_t length_);
 
-    //  Properties received from ZMTP peer.
-    metadata_t::dict_t zmtp_properties;
-
-    //  Properties received from ZAP server.
-    metadata_t::dict_t zap_properties;
-
     const options_t options;
 
   private:
+    //  Properties received from ZMTP peer.
+    metadata_t::dict_t _zmtp_properties;
+
+    //  Properties received from ZAP server.
+    metadata_t::dict_t _zap_properties;
+
     blob_t _routing_id;
 
     blob_t _user_id;