diff --git a/lib/iruby/comm.rb b/lib/iruby/comm.rb
index f72505f..3a712a2 100644
--- a/lib/iruby/comm.rb
+++ b/lib/iruby/comm.rb
@@ -13,17 +13,17 @@ def initialize(target_name, comm_id = SecureRandom.uuid)
       @target_name, @comm_id = target_name, comm_id
     end
 
-    def open(**data)
-      Kernel.instance.session.send(:publish, :comm_open, comm_id: @comm_id, data: data, target_name: @target_name)
+    def open(metadata = nil, **data)
+      Kernel.instance.session.send(:publish, :comm_open, metadata, comm_id: @comm_id, data: data, target_name: @target_name)
       Comm.comm[@comm_id] = self
     end
 
-    def send(**data)
-      Kernel.instance.session.send(:publish, :comm_msg, comm_id: @comm_id, data: data)
+    def send(metadata = nil, **data)
+      Kernel.instance.session.send(:publish, :comm_msg, metadata, comm_id: @comm_id, data: data)
     end
 
-    def close(**data)
-      Kernel.instance.session.send(:publish, :comm_close, comm_id: @comm_id, data: data)
+    def close(metadata = nil, **data)
+      Kernel.instance.session.send(:publish, :comm_close, metadata, comm_id: @comm_id, data: data)
       Comm.comm.delete(@comm_id)
     end
 
diff --git a/lib/iruby/session.rb b/lib/iruby/session.rb
index 584de9a..3a4c66d 100644
--- a/lib/iruby/session.rb
+++ b/lib/iruby/session.rb
@@ -70,7 +70,7 @@ def setup_security
       end
     end
 
-    def send(socket_type, message_type, content)
+    def send(socket_type, message_type, metadata = nil, content)
       sock = check_socket_type(socket_type)
       idents = if socket_type == :reply && @last_recvd_msg
                  @last_recvd_msg[:idents]
@@ -85,7 +85,7 @@ def send(socket_type, message_type, content)
         session:  @session_id,
         version:  '5.0'
       }
-      @adapter.send(sock, serialize(idents, header, content))
+      @adapter.send(sock, serialize(idents, header, metadata, content))
     end
 
     def recv(socket_type)
diff --git a/lib/iruby/session/mixin.rb b/lib/iruby/session/mixin.rb
index 5aed699..3ddd06c 100644
--- a/lib/iruby/session/mixin.rb
+++ b/lib/iruby/session/mixin.rb
@@ -4,10 +4,10 @@ module SessionSerialize
 
     private
 
-    def serialize(idents, header, content)
+    def serialize(idents, header, metadata = nil, content)
       msg = [MultiJson.dump(header),
              MultiJson.dump(@last_recvd_msg ? @last_recvd_msg[:header] : {}),
-             '{}',
+             MultiJson.dump(metadata || {}),
              MultiJson.dump(content || {})]
       frames = ([*idents].compact.map(&:to_s) << DELIM << sign(msg)) + msg
       IRuby.logger.debug "Sent #{frames.inspect}"