diff --git a/lib/set.rb b/lib/set.rb
index 95dd9217b1..cf99ffac4b 100644
--- a/lib/set.rb
+++ b/lib/set.rb
@@ -216,6 +216,9 @@
 #   has been modified while an element in the set.
 #
 class Set
+
+  VERSION = "1.0.3"
+
   include Enumerable
 
   # Creates a new set containing the given objects.
diff --git a/lib/set/set.gemspec b/lib/set/set.gemspec
index 1e83287420..c415fac99c 100644
--- a/lib/set/set.gemspec
+++ b/lib/set/set.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          = "set"
-  spec.version       = "1.0.3"
+  spec.name          = name
+  spec.version       = version
   spec.authors       = ["Akinori MUSHA"]
   spec.email         = ["knu@idaemons.org"]