diff --git a/dyndnsd.gemspec b/dyndnsd.gemspec
index ff153e4..2cf6ca0 100644
--- a/dyndnsd.gemspec
+++ b/dyndnsd.gemspec
@@ -44,7 +44,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'rack-test'
   s.add_development_dependency 'rake'
   s.add_development_dependency 'rspec'
-  s.add_development_dependency 'rubocop', '~> 1.75.1'
+  s.add_development_dependency 'rubocop', '~> 1.76.1'
   s.add_development_dependency 'rubocop-rake', '~> 0.7.1'
   s.add_development_dependency 'rubocop-rspec', '~> 3.6.0'
   s.add_development_dependency 'solargraph', '~> 0.55.0'
diff --git a/lib/dyndnsd/updater/zone_transfer_server.rb b/lib/dyndnsd/updater/zone_transfer_server.rb
index e04ba22..cf4bde5 100644
--- a/lib/dyndnsd/updater/zone_transfer_server.rb
+++ b/lib/dyndnsd/updater/zone_transfer_server.rb
@@ -89,7 +89,7 @@ module Dyndnsd
       # @return [Array{Array{Object}}]
       def self.parse_endpoints(endpoint_list)
         endpoint_list.map { |addr_string| addr_string.split('@') }
-                     .map { |addr_parts| [addr_parts[0], addr_parts[1].to_i || 53] }
+                     .map { |addr_parts| [addr_parts[0], addr_parts[1]&.to_i || 53] }
                      .map { |addr| [:tcp, :udp].map { |type| [type] + addr } }
                      .flatten(1)
       end