diff --git lib/pstore.rb lib/pstore.rb
index 3114eb5..7067f5c 100644
--- lib/pstore.rb
+++ lib/pstore.rb
@@ -119,7 +119,7 @@ class PStore
   # PStore objects are always reentrant. But if _thread_safe_ is set to true,
   # then it will become thread-safe at the cost of a minor performance hit.
   #
-  def initialize(file, thread_safe = false)
+  def initialize(file)
     dir = File::dirname(file)
     unless File::directory? dir
       raise PStore::Error, format("directory %s does not exist", dir)
@@ -130,7 +130,6 @@ class PStore
     @filename = file
     @abort = false
     @ultra_safe = false
-    @thread_safe = thread_safe
     @lock = Mutex.new
   end
 
@@ -313,7 +312,6 @@ class PStore
   #
   def transaction(read_only = false, &block)  # :yields:  pstore
     value = nil
-    raise PStore::Error, "nested transaction" if !@thread_safe && @lock.locked?
     @lock.synchronize do
       @rdonly = read_only
       @abort = false
diff --git test/test_pstore.rb test/test_pstore.rb
index 32d79ea..fdd85ae 100644
--- test/test_pstore.rb
+++ test/test_pstore.rb
@@ -73,20 +73,8 @@ class PStoreTest < Test::Unit::TestCase
   end
 
   def test_thread_safe
-    assert_raise(PStore::Error) do
-      flag = false
-      Thread.new do
-        @pstore.transaction do
-          @pstore[:foo] = "bar"
-          flag = true
-          sleep 1
-        end
-      end
-      until flag; end
-      @pstore.transaction {}
-    end
     assert_block do
-      pstore = PStore.new("pstore.tmp2.#{Process.pid}",true)
+      pstore = PStore.new("pstore.tmp2.#{Process.pid}")
       flag = false
       Thread.new do
         pstore.transaction do