diff --git a/lib/ably/realtime/client.rb b/lib/ably/realtime/client.rb
index 4ca31fe6..5a3317e4 100644
--- a/lib/ably/realtime/client.rb
+++ b/lib/ably/realtime/client.rb
@@ -62,7 +62,7 @@ class Client
 
       # When a recover option is specified a connection inherits the state of a previous connection that may have existed under a different instance of the Realtime library, please refer to the API documentation for further information on connection state recovery
       # @return [String,Nil]
-      attr_reader :recover
+      attr_accessor :recover
 
       # Additional parameters to be sent in the querystring when initiating a realtime connection
       # @return [Hash]
diff --git a/lib/ably/realtime/connection/connection_manager.rb b/lib/ably/realtime/connection/connection_manager.rb
index 00e66622..69044113 100644
--- a/lib/ably/realtime/connection/connection_manager.rb
+++ b/lib/ably/realtime/connection/connection_manager.rb
@@ -111,6 +111,14 @@ def connected(protocol_message)
         # Update the connection details and any associated defaults
         connection.set_connection_details protocol_message.connection_details
 
+        is_connection_resume_or_recover_attempt = !connection.key.nil? || !client.recover.nil?
+        # RTN15c7, RTN16d
+        failed_resume_or_recover = !protocol_message.connection_id == connection.id && !protocol_message.error.nil?
+        if is_connection_resume_or_recover_attempt and failed_resume_or_recover # RTN15c7
+          connection.message_serial = 0
+        end
+        client.recover = nil # RTN16k, explicitly setting null, so it won't be used for subsequent connection requests
+
         if connection.key
           if protocol_message.connection_id == connection.id
             logger.debug { "ConnectionManager: Connection resumed successfully - ID #{connection.id} and key #{connection.key}" }