diff --git a/History.md b/History.md
index 516e25a8..b33b310b 100644
--- a/History.md
+++ b/History.md
@@ -9,6 +9,7 @@
 
 * Bugfixes
   * Your bugfix goes here <Most recent on the top, like GitHub> (#Github Number)
+  * Ignore Rails' reaper thread (and any thread marked forksafe) for warning ([#2475])
   * Ignore illegal (by Rack spec) response header ([#2439])
   * Close idle connections immediately on shutdown ([#2460])
   * Fix some instances of phased restart errors related to the `json` gem (#2473)
diff --git a/lib/puma/cluster.rb b/lib/puma/cluster.rb
index 189a9267..c2eff7da 100644
--- a/lib/puma/cluster.rb
+++ b/lib/puma/cluster.rb
@@ -331,13 +331,15 @@ module Puma
 
       log "* Process workers: #{@options[:workers]}"
 
-      before = Thread.list
+      # Threads explicitly marked as fork safe will be ignored.
+      # Used in Rails, but may be used by anyone.
+      before = Thread.list.reject { |t| t.thread_variable_get(:fork_safe) }
 
       if preload?
         log "* Preloading application"
         load_and_bind
 
-        after = Thread.list
+        after = Thread.list.reject { |t| t.thread_variable_get(:fork_safe) }
 
         if after.size > before.size
           threads = (after - before)