diff --git a/lib/net/imap.rb b/lib/net/imap.rb
index 278913a7..2d005c92 100644
--- a/lib/net/imap.rb
+++ b/lib/net/imap.rb
@@ -1131,28 +1131,27 @@ def tls_verified?; @tls_verified end
 
     # Disconnects from the server.
     #
+    # Waits for receiver thread to close before returning.  Slow or stuck
+    # response handlers can cause #disconnect to hang until they complete.
+    #
     # Related: #logout, #logout!
     def disconnect
+      in_logout_state = try_state_logout?
       return if disconnected?
-      state_logout!
       begin
-        begin
-          # try to call SSL::SSLSocket#io.
-          @sock.io.shutdown
-        rescue NoMethodError
-          # @sock is not an SSL::SSLSocket.
-          @sock.shutdown
-        end
+        @sock.to_io.shutdown
       rescue Errno::ENOTCONN
         # ignore `Errno::ENOTCONN: Socket is not connected' on some platforms.
       rescue Exception => e
         @receiver_thread.raise(e)
       end
+      @sock.close
       @receiver_thread.join
-      synchronize do
-        @sock.close
-      end
       raise e if e
+    ensure
+      # Try again after shutting down the receiver thread.  With no reciever
+      # left to wait for, any remaining locks should be _very_ brief.
+      state_logout! unless in_logout_state
     end
 
     # Returns true if disconnected from the server.
@@ -3363,8 +3362,6 @@ def start_receiver_thread
       rescue Exception => ex
         @receiver_thread_exception = ex
         # don't exit the thread with an exception
-      ensure
-        state_logout!
       end
     end
 
@@ -3446,6 +3443,8 @@ def receive_responses
           @idle_done_cond.signal
         end
       end
+    ensure
+      state_logout!
     end
 
     def get_tagged_response(tag, cmd, timeout = nil)
@@ -3808,15 +3807,29 @@ def state_selected!
     end
 
     def state_unselected!
-      state_authenticated! if connection_state.to_sym == :selected
+      synchronize do
+        state_authenticated! if connection_state.to_sym == :selected
+      end
     end
 
     def state_logout!
+      return true if connection_state in [:logout, *]
       synchronize do
+        return true if connection_state in [:logout, *]
         @connection_state = ConnectionState::Logout.new
       end
     end
 
+    # don't wait to aqcuire the lock
+    def try_state_logout?
+      return true if connection_state in [:logout, *]
+      return false unless acquired_lock = mon_try_enter
+      state_logout!
+      true
+    ensure
+      mon_exit if acquired_lock
+    end
+
     def sasl_adapter
       SASLAdapter.new(self, &method(:send_command_with_continuations))
     end