diff --git a/activerecord/test/cases/base_test.rb b/activerecord/test/cases/base_test.rb
index 983bcd98260b2..ef1ebbb400c85 100644
--- a/activerecord/test/cases/base_test.rb
+++ b/activerecord/test/cases/base_test.rb
@@ -1380,6 +1380,8 @@ def test_marshal_between_processes
       })
 
       rd, wr = IO.pipe
+      rd.binmode
+      wr.binmode
 
       ActiveRecord::Base.connection_handler.clear_all_connections!
 
diff --git a/activerecord/test/cases/connection_management_test.rb b/activerecord/test/cases/connection_management_test.rb
index 00667cc52e174..77d9ae9b8eb01 100644
--- a/activerecord/test/cases/connection_management_test.rb
+++ b/activerecord/test/cases/connection_management_test.rb
@@ -31,6 +31,8 @@ def test_connection_pool_per_pid
           object_id = ActiveRecord::Base.connection.object_id
 
           rd, wr = IO.pipe
+          rd.binmode
+          wr.binmode
 
           pid = fork {
             rd.close
diff --git a/activesupport/lib/active_support/testing/isolation.rb b/activesupport/lib/active_support/testing/isolation.rb
index 75ead48376348..908af176be0ed 100644
--- a/activesupport/lib/active_support/testing/isolation.rb
+++ b/activesupport/lib/active_support/testing/isolation.rb
@@ -37,6 +37,8 @@ def run
       module Forking
         def run_in_isolation(&blk)
           read, write = IO.pipe
+          read.binmode
+          write.binmode
 
           pid = fork do
             read.close