diff --git a/lib/tsort.gemspec b/lib/tsort.gemspec
index a82393b70b892a..bd1f55ec7a3018 100644
--- a/lib/tsort.gemspec
+++ b/lib/tsort.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          = "tsort"
-  spec.version       = "0.1.1"
+  spec.name          = name
+  spec.version       = version
   spec.authors       = ["Tanaka Akira"]
   spec.email         = ["akr@fsij.org"]
 
diff --git a/lib/tsort.rb b/lib/tsort.rb
index 00ee609d64e2e9..3a2a91a7b4f18c 100644
--- a/lib/tsort.rb
+++ b/lib/tsort.rb
@@ -122,6 +122,9 @@
 #
 
 module TSort
+
+  VERSION = "0.1.1"
+
   class Cyclic < StandardError
   end