diff --git a/lib/net/imap/sasl/cram_md5_authenticator.rb b/lib/net/imap/sasl/cram_md5_authenticator.rb
index 42935d3a..6a6242eb 100644
--- a/lib/net/imap/sasl/cram_md5_authenticator.rb
+++ b/lib/net/imap/sasl/cram_md5_authenticator.rb
@@ -21,13 +21,18 @@ def initialize(user, password, warn_deprecation: true, **_ignored)
     require "digest/md5"
     @user = user
     @password = password
+    @done = false
   end
 
   def process(challenge)
     digest = hmac_md5(challenge, @password)
     return @user + " " + digest
+  ensure
+    @done = true
   end
 
+  def done?; @done end
+
   private
 
   def hmac_md5(text, key)
diff --git a/lib/net/imap/sasl/login_authenticator.rb b/lib/net/imap/sasl/login_authenticator.rb
index 11d508df..f13cac6a 100644
--- a/lib/net/imap/sasl/login_authenticator.rb
+++ b/lib/net/imap/sasl/login_authenticator.rb
@@ -20,7 +20,8 @@
 class Net::IMAP::SASL::LoginAuthenticator
   STATE_USER = :USER
   STATE_PASSWORD = :PASSWORD
-  private_constant :STATE_USER, :STATE_PASSWORD
+  STATE_DONE = :DONE
+  private_constant :STATE_USER, :STATE_PASSWORD, :STATE_DONE
 
   def initialize(user, password, warn_deprecation: true, **_ignored)
     if warn_deprecation
@@ -37,7 +38,12 @@ def process(data)
       @state = STATE_PASSWORD
       return @user
     when STATE_PASSWORD
+      @state = STATE_DONE
       return @password
+    when STATE_DONE
+      raise ResponseParseError, data
     end
   end
+
+  def done?; @state == STATE_DONE end
 end