Index: lib/pstore.rb
===================================================================
--- lib/pstore.rb	(revision 33263)
+++ lib/pstore.rb	(working copy)
@@ -363,7 +363,7 @@
   def open_and_lock_file(filename, read_only)
     if read_only
       begin
-        file = File.new(filename, RD_ACCESS)
+        file = File.new(filename, RD_ACCESS, external_encoding: Encoding::BINARY)
         begin
           file.flock(File::LOCK_SH)
           return file
@@ -375,7 +375,7 @@
         return nil
       end
     else
-      file = File.new(filename, RDWR_ACCESS)
+      file = File.new(filename, RDWR_ACCESS, external_encoding: Encoding::BINARY)
       file.flock(File::LOCK_EX)
       return file
     end
Index: test/test_pstore.rb
===================================================================
--- test/test_pstore.rb	(revision 33263)
+++ test/test_pstore.rb	(working copy)
@@ -110,4 +110,13 @@
       pstore.transaction { pstore.transaction { } }
     end
   end
+
+  # Test that PStore's file operations do not blow up when default encodings are set
+  def test_pstore_files_are_accessed_as_binary_files
+    Encoding.default_internal = 'utf-8'
+    Encoding.default_external = 'utf-8'
+    (1..1000).each do |i|
+      @pstore.transaction { @pstore["Key#{i}"] = "value #{i}" } 
+    end
+  end
 end