diff --git a/ChangeLog b/ChangeLog
index 3a31420d77..a579b53459 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Jun 28 22:55:00 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/pstore.rb (PStore::CHECKSUM_ALGO): extract the algorithm for
+	  checksum, instead of qualified names for each times.
+
 Tue Jun 28 22:29:36 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* bootstraptest/runner.rb: do not use safe navigation operator.
diff --git a/lib/pstore.rb b/lib/pstore.rb
index 8dfcaec7df..66a919e189 100644
--- a/lib/pstore.rb
+++ b/lib/pstore.rb
@@ -352,9 +352,10 @@ class PStore
 
   private
   # Constant for relieving Ruby's garbage collector.
+  CHECKSUM_ALGO = Digest::MD5
   EMPTY_STRING = ""
   EMPTY_MARSHAL_DATA = Marshal.dump({})
-  EMPTY_MARSHAL_CHECKSUM = Digest::MD5.digest(EMPTY_MARSHAL_DATA)
+  EMPTY_MARSHAL_CHECKSUM = CHECKSUM_ALGO.digest(EMPTY_MARSHAL_DATA)
 
   #
   # Open the specified filename (either in read-only mode or in
@@ -409,7 +410,7 @@ class PStore
         size = empty_marshal_data.bytesize
       else
         table = load(data)
-        checksum = Digest::MD5.digest(data)
+        checksum = CHECKSUM_ALGO.digest(data)
         size = data.bytesize
         raise Error, "PStore file seems to be corrupted." unless table.is_a?(Hash)
       end
@@ -429,7 +430,7 @@ class PStore
   def save_data(original_checksum, original_file_size, file)
     new_data = dump(@table)
 
-    if new_data.bytesize != original_file_size || Digest::MD5.digest(new_data) != original_checksum
+    if new_data.bytesize != original_file_size || CHECKSUM_ALGO.digest(new_data) != original_checksum
       if @ultra_safe && !on_windows?
         # Windows doesn't support atomic file renames.
         save_data_with_atomic_file_rename_strategy(new_data, file)