diff --git a/ruby_header_parser.gemspec b/ruby_header_parser.gemspec
index db211cd..f17403e 100644
--- a/ruby_header_parser.gemspec
+++ b/ruby_header_parser.gemspec
@@ -37,6 +37,7 @@ Gem::Specification.new do |spec|
   # spec.add_dependency "example-gem", "~> 1.0"
 
   spec.add_development_dependency "rake"
+  spec.add_development_dependency "rbs", ">= 3.7.0"
   spec.add_development_dependency "rspec"
   spec.add_development_dependency "rspec-its"
   spec.add_development_dependency "rspec-parameterized"
diff --git a/sig/non-gemify/io.rbs b/sig/non-gemify/io.rbs
deleted file mode 100644
index bec29bb..0000000
--- a/sig/non-gemify/io.rbs
+++ /dev/null
@@ -1,4 +0,0 @@
-class IO
-  def readlines: (?String sep, ?Integer limit, ?chomp: bool) -> ::Array[String]
-    | ...
-end
diff --git a/sig/non-gemify/kernel.rbs b/sig/non-gemify/kernel.rbs
deleted file mode 100644
index 3f62d33..0000000
--- a/sig/non-gemify/kernel.rbs
+++ /dev/null
@@ -1,6 +0,0 @@
-module Kernel
-  # FIXME: monkey patch for `exception` arg of `Kernel.system`
-  def self?.system: (String command, *String args, ?unsetenv_others: boolish, ?pgroup: true | Integer, ?umask: Integer, ?in: redirect_fd, ?out: redirect_fd, ?err: redirect_fd, ?close_others: boolish, ?chdir: String, ?exception: bool) -> (NilClass | FalseClass | TrueClass)
-    | (Hash[string, string?] env, String command, *String args, ?unsetenv_others: boolish, ?pgroup: true | Integer, ?umask: Integer, ?in: redirect_fd, ?out: redirect_fd, ?err: redirect_fd, ?close_others: boolish, ?chdir: String, ?exception: bool) -> (NilClass | FalseClass | TrueClass)
-    | ...
-end