diff --git a/lib/fluent/plugin_helper/retry_state.rb b/lib/fluent/plugin_helper/retry_state.rb
index 687e8052f3..7851fd61ea 100644
--- a/lib/fluent/plugin_helper/retry_state.rb
+++ b/lib/fluent/plugin_helper/retry_state.rb
@@ -159,7 +159,7 @@ def naive_next_time(retry_next_times)
         def calc_max_retry_timeout(max_steps)
           result = 0
           max_steps.times { |i|
-            result += calc_interval(i)
+            result += calc_interval(i + 1)
           }
           result
         end
diff --git a/test/plugin_helper/test_retry_state.rb b/test/plugin_helper/test_retry_state.rb
index 616cc8671d..4edd41bdf9 100644
--- a/test/plugin_helper/test_retry_state.rb
+++ b/test/plugin_helper/test_retry_state.rb
@@ -413,7 +413,7 @@ class Dummy < Fluent::Plugin::TestBase
     override_current_time(s, dummy_current_time)
 
     timeout = 0
-    5.times { |i| timeout += 1.0 * (2 ** (i - 1)) }
+    5.times { |i| timeout += 1.0 * (2 ** i) }
 
     assert_equal dummy_current_time, s.current_time
     assert_equal (dummy_current_time + 100), s.timeout_at