diff --git a/lib/winrm/shells/base.rb b/lib/winrm/shells/base.rb
index 7bb86637..3d11ac49 100644
--- a/lib/winrm/shells/base.rb
+++ b/lib/winrm/shells/base.rb
@@ -183,6 +183,10 @@ def add_finalizer
       def remove_finalizer
         ObjectSpace.undefine_finalizer(self)
       end
+
+      def self.finalize(connection_opts, transport, shell_id)
+        proc { Thread.new { close_shell(connection_opts, transport, shell_id) } }
+      end
     end
   end
 end
diff --git a/lib/winrm/shells/cmd.rb b/lib/winrm/shells/cmd.rb
index d32dd665..07ff8a92 100644
--- a/lib/winrm/shells/cmd.rb
+++ b/lib/winrm/shells/cmd.rb
@@ -20,10 +20,6 @@ module Shells
     class Cmd < Base
       include WinRM::WSMV::SOAP
       class << self
-        def finalize(connection_opts, transport, shell_id)
-          proc { Cmd.close_shell(connection_opts, transport, shell_id) }
-        end
-
         def close_shell(connection_opts, transport, shell_id)
           msg = WinRM::WSMV::CloseShell.new(connection_opts, shell_id: shell_id)
           transport.send_request(msg.build)
diff --git a/lib/winrm/shells/power_shell.rb b/lib/winrm/shells/power_shell.rb
index d9ca50d2..696ede9f 100644
--- a/lib/winrm/shells/power_shell.rb
+++ b/lib/winrm/shells/power_shell.rb
@@ -29,10 +29,6 @@ class Powershell < Base
       include WinRM::WSMV::SOAP
 
       class << self
-        def finalize(connection_opts, transport, shell_id)
-          proc { Powershell.close_shell(connection_opts, transport, shell_id) }
-        end
-
         def close_shell(connection_opts, transport, shell_id)
           msg = WinRM::WSMV::CloseShell.new(
             connection_opts,