diff --git a/lib/pp.gemspec b/lib/pp.gemspec
index 3f08f400c4..27a92a8ce4 100644
--- a/lib/pp.gemspec
+++ b/lib/pp.gemspec
@@ -1,6 +1,13 @@
+name = File.basename(__FILE__, ".gemspec")
+version = ["lib", Array.new(name.count("-")+1).join("/")].find do |dir|
+  break File.foreach(File.join(__dir__, dir, "#{name.tr('-', '/')}.rb")) do |line|
+    /^\s*VERSION\s*=\s*"(.*)"/ =~ line and break $1
+  end rescue nil
+end
+
 Gem::Specification.new do |spec|
-  spec.name          = "pp"
-  spec.version       = "0.4.0"
+  spec.name          = name
+  spec.version       = version
   spec.authors       = ["Tanaka Akira"]
   spec.email         = ["akr@fsij.org"]
 
diff --git a/lib/pp.rb b/lib/pp.rb
index 81551aa116..b81f84cec5 100644
--- a/lib/pp.rb
+++ b/lib/pp.rb
@@ -61,6 +61,9 @@ require 'prettyprint'
 # Tanaka Akira <akr@fsij.org>
 
 class PP < PrettyPrint
+
+  VERSION = "0.4.0"
+
   # Returns the usable width for +out+.
   # As the width of +out+:
   # 1. If +out+ is assigned to a tty device, its width is used.