diff --git a/mrbgems/mruby-socket/test/addrinfo.rb b/mrbgems/mruby-socket/test/addrinfo.rb
index 491656179..ce70a984c 100644
--- a/mrbgems/mruby-socket/test/addrinfo.rb
+++ b/mrbgems/mruby-socket/test/addrinfo.rb
@@ -6,6 +6,27 @@ assert('super class of Addrinfo') do
   assert_equal(Object, Addrinfo.superclass)
 end
 
+# TEMPORARY DIAGNOSTIC: observe which getaddrinfo pattern works on Windows CI.
+# Remove once the root cause is identified and the real fix is in place.
+assert('Addrinfo.getaddrinfo diagnostic') do
+  cases = [
+    ['127.0.0.1 literal AF_INET', -> { Addrinfo.getaddrinfo('127.0.0.1', 53, Socket::AF_INET, Socket::SOCK_STREAM) }],
+    ['localhost AF_UNSPEC',       -> { Addrinfo.getaddrinfo('localhost', 53, Socket::AF_UNSPEC, Socket::SOCK_STREAM) }],
+    ['localhost nil family',      -> { Addrinfo.getaddrinfo('localhost', 53) }],
+    ['localhost AF_INET6',        -> { Addrinfo.getaddrinfo('localhost', 53, Socket::AF_INET6, Socket::SOCK_STREAM) }],
+    ['localhost AF_INET (orig)',  -> { Addrinfo.getaddrinfo('localhost', 53, Socket::AF_INET, Socket::SOCK_STREAM) }],
+  ]
+  cases.each do |label, probe|
+    begin
+      ary = probe.call
+      puts "DIAG #{label}: OK size=#{ary.size} first=#{ary.first&.ip_address.inspect}"
+    rescue => e
+      puts "DIAG #{label}: #{e.class} #{e.message}"
+    end
+  end
+  assert_true(true)
+end
+
 assert('Addrinfo.getaddrinfo') do
   ary = Addrinfo.getaddrinfo("localhost", 53, Socket::AF_INET, Socket::SOCK_STREAM)
   assert_true(ary.size >= 1)