diff --git a/lib/pstore.rb b/lib/pstore.rb
index d717820..5e33035 100644
--- a/lib/pstore.rb
+++ b/lib/pstore.rb
@@ -126,6 +126,7 @@ class PStore
     @filename = file
     @abort = false
     @ultra_safe = false
+    @modified = false
     @thread_safe = thread_safe
     @lock = Mutex.new
   end
@@ -141,6 +142,7 @@ class PStore
   def in_transaction_wr
     in_transaction
     raise PStore::Error, "in read-only transaction" if @rdonly
+    @modified = true
   end
   private :in_transaction, :in_transaction_wr
 
@@ -313,17 +315,18 @@ class PStore
     @lock.synchronize do
       @rdonly = read_only
       @abort = false
+      @modified = false
       file = open_and_lock_file(@filename, read_only)
       if file
         begin
-          @table, checksum, original_data_size = load_data(file, read_only)
+          @table = load_data(file)
 
           catch(:pstore_abort_transaction) do
             value = yield(self)
           end
 
           if !@abort && !read_only
-            save_data(checksum, original_data_size, file)
+            save_data(file)
           end
         ensure
           file.close if !file.closed?
@@ -342,7 +345,7 @@ class PStore
   end
 
   private
-  # Constant for relieving Ruby's garbage collector.
+  # Constants for compatibility.
   EMPTY_STRING = ""
   EMPTY_MARSHAL_DATA = Marshal.dump({})
   EMPTY_MARSHAL_CHECKSUM = Digest::MD5.digest(EMPTY_MARSHAL_DATA)
@@ -378,35 +381,16 @@ class PStore
   end
 
   # Load the given PStore file.
-  # If +read_only+ is true, the unmarshalled Hash will be returned.
-  # If +read_only+ is false, a 3-tuple will be returned: the unmarshalled
-  # Hash, an MD5 checksum of the data, and the size of the data.
-  def load_data(file, read_only)
-    if read_only
-      begin
-        table = load(file)
-        raise Error, "PStore file seems to be corrupted." unless table.is_a?(Hash)
-      rescue EOFError
-        # This seems to be a newly-created file.
-        table = {}
-      end
-      table
-    else
-      data = file.read
-      if data.empty?
-        # This seems to be a newly-created file.
-        table = {}
-        checksum = empty_marshal_checksum
-        size = empty_marshal_data.bytesize
-      else
-        table = load(data)
-        checksum = Digest::MD5.digest(data)
-        size = data.bytesize
-        raise Error, "PStore file seems to be corrupted." unless table.is_a?(Hash)
-      end
-      data.replace(EMPTY_STRING)
-      [table, checksum, size]
+  # The unmarshalled Hash will be returned.
+  def load_data(file)
+    begin
+      table = load(file)
+      raise Error, "PStore file seems to be corrupted." unless table.is_a?(Hash)
+    rescue EOFError
+      # This seems to be a newly-created file.
+      table = {}
     end
+    table
   end
 
   def on_windows?
@@ -417,10 +401,10 @@ class PStore
     is_windows
   end
 
-  def save_data(original_checksum, original_file_size, file)
+  def save_data(file)
     new_data = dump(@table)
 
-    if new_data.bytesize != original_file_size || Digest::MD5.digest(new_data) != original_checksum
+    if @modified
       if @ultra_safe && !on_windows?
         # Windows doesn't support atomic file renames.
         save_data_with_atomic_file_rename_strategy(new_data, file)
@@ -429,7 +413,7 @@ class PStore
       end
     end
 
-    new_data.replace(EMPTY_STRING)
+    new_data.clear
   end
 
   def save_data_with_atomic_file_rename_strategy(data, file)