diff --git a/Steepfile b/Steepfile
index 60689d543..b00e4542b 100644
--- a/Steepfile
+++ b/Steepfile
@@ -15,6 +15,7 @@ target :lib do
   signature "stdlib/rdoc/0/"
   signature "stdlib/ripper/0"
   signature "stdlib/pp/0"
+  signature "steep/patch.rbs"
 
   # configure_code_diagnostics do |config|
   #   config[D::Ruby::MethodDefinitionMissing] = :hint
diff --git a/core/module.rbs b/core/module.rbs
index c5e43339c..b585bc43c 100644
--- a/core/module.rbs
+++ b/core/module.rbs
@@ -1646,6 +1646,43 @@ class Module < Object
   #
   def remove_method: (*interned arg0) -> self
 
+  # <!--
+  #   rdoc-file=vm_method.c
+  #   - ruby2_keywords(method_name, ...)    -> nil
+  # -->
+  # For the given method names, marks the method as passing keywords through a
+  # normal argument splat.  This should only be called on methods that accept an
+  # argument splat (`*args`) but not explicit keywords or a keyword splat.  It
+  # marks the method such that if the method is called with keyword arguments, the
+  # final hash argument is marked with a special flag such that if it is the final
+  # element of a normal argument splat to another method call, and that method
+  # call does not include explicit keywords or a keyword splat, the final element
+  # is interpreted as keywords. In other words, keywords will be passed through
+  # the method to other methods.
+  #
+  # This should only be used for methods that delegate keywords to another method,
+  # and only for backwards compatibility with Ruby versions before 3.0. See
+  # https://www.ruby-lang.org/en/news/2019/12/12/separation-of-positional-and-keyw
+  # ord-arguments-in-ruby-3-0/ for details on why `ruby2_keywords` exists and when
+  # and how to use it.
+  #
+  # This method will probably be removed at some point, as it exists only for
+  # backwards compatibility. As it does not exist in Ruby versions before 2.7,
+  # check that the module responds to this method before calling it:
+  #
+  #     module Mod
+  #       def foo(meth, *args, &block)
+  #         send(:"do_#{meth}", *args, &block)
+  #       end
+  #       ruby2_keywords(:foo) if respond_to?(:ruby2_keywords, true)
+  #     end
+  #
+  # However, be aware that if the `ruby2_keywords` method is removed, the behavior
+  # of the `foo` method using the above approach will change so that the method
+  # does not pass through keywords.
+  #
+  private def ruby2_keywords: (*interned method_name) -> nil
+
   # <!--
   #   rdoc-file=object.c
   #   - mod.set_temporary_name(string) -> self
diff --git a/core/proc.rbs b/core/proc.rbs
index bdd88d92b..e1828e123 100644
--- a/core/proc.rbs
+++ b/core/proc.rbs
@@ -831,6 +831,37 @@ class Proc
   #
   def parameters: (?lambda: boolish) -> Method::param_types
 
+  # <!--
+  #   rdoc-file=proc.c
+  #   - proc.ruby2_keywords -> proc
+  # -->
+  # Marks the proc as passing keywords through a normal argument splat. This
+  # should only be called on procs that accept an argument splat (`*args`) but not
+  # explicit keywords or a keyword splat.  It marks the proc such that if the proc
+  # is called with keyword arguments, the final hash argument is marked with a
+  # special flag such that if it is the final element of a normal argument splat
+  # to another method call, and that method call does not include explicit
+  # keywords or a keyword splat, the final element is interpreted as keywords.  In
+  # other words, keywords will be passed through the proc to other methods.
+  #
+  # This should only be used for procs that delegate keywords to another method,
+  # and only for backwards compatibility with Ruby versions before 2.7.
+  #
+  # This method will probably be removed at some point, as it exists only for
+  # backwards compatibility. As it does not exist in Ruby versions before 2.7,
+  # check that the proc responds to this method before calling it. Also, be aware
+  # that if this method is removed, the behavior of the proc will change so that
+  # it does not pass through keywords.
+  #
+  #     module Mod
+  #       foo = ->(meth, *args, &block) do
+  #         send(:"do_#{meth}", *args, &block)
+  #       end
+  #       foo.ruby2_keywords if foo.respond_to?(:ruby2_keywords)
+  #     end
+  #
+  def ruby2_keywords: () -> self
+
   # <!--
   #   rdoc-file=proc.c
   #   - prc.source_location  -> [String, Integer, Integer, Integer, Integer]
diff --git a/sig/unit_test/spy.rbs b/sig/unit_test/spy.rbs
index de3f37ddb..c62602f29 100644
--- a/sig/unit_test/spy.rbs
+++ b/sig/unit_test/spy.rbs
@@ -20,11 +20,3 @@ module RBS
     end
   end
 end
-
-class Proc
-  def ruby2_keywords: () -> self
-end
-
-class Module
-  def ruby2_keywords: (*Symbol) -> void
-end
diff --git a/steep/patch.rbs b/steep/patch.rbs
new file mode 100644
index 000000000..4bbacff42
--- /dev/null
+++ b/steep/patch.rbs
@@ -0,0 +1,9 @@
+# Remove here if duplicated
+
+class Module
+  def ruby2_keywords: (*untyped) -> void
+end
+
+class Proc
+  def ruby2_keywords: () -> self
+end
diff --git a/test/stdlib/Module_test.rb b/test/stdlib/Module_test.rb
index b1f1cce48..d4b285333 100644
--- a/test/stdlib/Module_test.rb
+++ b/test/stdlib/Module_test.rb
@@ -25,6 +25,9 @@ class ModuleInstanceTest < Test::Unit::TestCase
 
   module Foo
     BAR = 1
+
+    def foo(meth, *args, &block)
+    end
   end
 
   def test_include
@@ -412,6 +415,13 @@ def test_attr_accessor
     )
   end
 
+  def test_ruby2_keywords
+    assert_send_type(
+      "(Symbol) -> nil",
+      Foo, :ruby2_keywords, :foo
+    )
+  end
+
   def test_set_temporary_name
     mod = Module.new
 
diff --git a/test/stdlib/Proc_test.rb b/test/stdlib/Proc_test.rb
index 481c60535..90310f527 100644
--- a/test/stdlib/Proc_test.rb
+++ b/test/stdlib/Proc_test.rb
@@ -138,6 +138,11 @@ def test_parameters
                       proc{|*, **, &b| }, :parameters
   end
 
+  def test_ruby2_keywords
+    assert_send_type '() -> ProcInstanceTest::MyProc',
+                     MyProc.new{}, :ruby2_keywords
+  end
+
   def test_source_location
     if_ruby(..."4.1") do
       assert_send_type  '() -> [String, Integer]',