diff --git a/ChangeLog b/ChangeLog
index cc8c2dbd55..a1ce83ada2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Tue Mar  8 08:13:01 2016  Rei Odaira  <Rei.Odaira@gmail.com>
+
+	* test/net/imap/test_imap.rb (test_idle_timeout): Because of the
+	  timeout specified in "imap.idle(0.2)", there is no gurantee that
+	  the server thread has done all the work before the client thread
+	  performs the assertions. It depends on the thread scheduling.
+	  Add checks to avoid false positives (on AIX, particularly).
+
 Tue Mar  8 00:42:22 2016  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* ruby.c (warn_cr_in_shebang): meaningless check on DOSISH platforms.
diff --git a/test/net/imap/test_imap.rb b/test/net/imap/test_imap.rb
index 3476b66c79..cdd9323c10 100644
--- a/test/net/imap/test_imap.rb
+++ b/test/net/imap/test_imap.rb
@@ -310,19 +310,31 @@ class IMAPTest < Test::Unit::TestCase
     begin
       imap = Net::IMAP.new(SERVER_ADDR, :port => port)
       responses = []
-        Thread.pass
+      Thread.pass
       imap.idle(0.2) do |res|
         responses.push(res)
       end
-      assert_equal(3, responses.length)
-      assert_instance_of(Net::IMAP::ContinuationRequest, responses[0])
-      assert_equal("EXISTS", responses[1].name)
-      assert_equal(3, responses[1].data)
-      assert_equal("EXPUNGE", responses[2].name)
-      assert_equal(2, responses[2].data)
-      assert_equal(2, requests.length)
-      assert_equal("RUBY0001 IDLE\r\n", requests[0])
-      assert_equal("DONE\r\n", requests[1])
+      # There is no gurantee that this thread has received all the responses,
+      # so check the response length.
+      if responses.length > 0
+        assert_instance_of(Net::IMAP::ContinuationRequest, responses[0])
+        if responses.length > 1
+          assert_equal("EXISTS", responses[1].name)
+          assert_equal(3, responses[1].data)
+          if responses.length > 2
+            assert_equal("EXPUNGE", responses[2].name)
+            assert_equal(2, responses[2].data)
+          end
+        end
+      end
+      # Also, there is no gurantee that the server thread has stored
+      # all the requests into the array, so check the length.
+      if requests.length > 0
+        assert_equal("RUBY0001 IDLE\r\n", requests[0])
+        if requests.length > 1
+          assert_equal("DONE\r\n", requests[1])
+        end
+      end
       imap.logout
     ensure
       imap.disconnect if imap