diff --git a/lib/net/imap/sasl/authenticators.rb b/lib/net/imap/sasl/authenticators.rb
index 88d5feb5..2abf2626 100644
--- a/lib/net/imap/sasl/authenticators.rb
+++ b/lib/net/imap/sasl/authenticators.rb
@@ -65,7 +65,7 @@ def names; @authenticators.keys end
     # When only a single argument is given, the authenticator class will be
     # lazily loaded from <tt>Net::IMAP::SASL::#{name}Authenticator</tt> (case is
     # preserved and non-alphanumeric characters are removed..
-    def add_authenticator(name, authenticator = nil)
+    def add_authenticator(name, authenticator = nil, warn_overwrite: true)
       key = name.upcase.to_sym
       authenticator ||= begin
         class_name = "#{name.gsub(/[^a-zA-Z0-9]/, "")}Authenticator".to_sym
@@ -75,6 +75,11 @@ def add_authenticator(name, authenticator = nil)
           auth_class.new(*creds, **props, &block)
         }
       end
+      if warn_overwrite && (original = @authenticators[key])
+        warn("%p: replacing existing %p authenticator: %p" % [
+          self, key, original
+        ], uplevel: 1)
+      end
       @authenticators[key] = authenticator
     end