diff --git a/lib/mathn.gemspec b/lib/mathn.gemspec
new file mode 100644
index 0000000000..3fbb466b8d
--- /dev/null
+++ b/lib/mathn.gemspec
@@ -0,0 +1,16 @@
+Gem::Specification.new do |s|
+  s.name = "mathn"
+  s.version = '0.0.1'
+  s.date = '2017-03-20'
+  s.summary = "Deprecated library that extends math operations."
+  s.description = "Deprecated library that extends math operations."
+
+  s.require_path = %w{lib}
+  s.files = %w{mathn.rb}
+  s.required_ruby_version = ">= 2.5.0dev"
+
+  s.authors = ["Keiju ISHITSUKA"]
+  s.email = [nil]
+  s.homepage = "https://www.ruby-lang.org"
+  s.license = "BSD-2-Clause"
+end