diff --git a/config/flay.yml b/config/flay.yml
index 47bf198e..860f2976 100644
--- a/config/flay.yml
+++ b/config/flay.yml
@@ -1,3 +1,3 @@
 ---
 threshold: 16
-total_score: 1309
+total_score: 1317
diff --git a/lib/mutest/mutator/node/arguments.rb b/lib/mutest/mutator/node/arguments.rb
index 8b7f6bcf..0718891b 100644
--- a/lib/mutest/mutator/node/arguments.rb
+++ b/lib/mutest/mutator/node/arguments.rb
@@ -13,6 +13,7 @@ class Arguments < self
         def dispatch
           emit_argument_presence
           emit_argument_mutations
+          emit_hash_type_hint
           emit_mlhs_expansion
         end
 
@@ -47,6 +48,22 @@ def invalid_argument_replacement?(mutest, index)
           n_arg?(mutest) && children[0...index].any?(&method(:n_optarg?))
         end
 
+        def emit_hash_type_hint
+          *first_args, last_arg = children
+
+          return unless last_arg && hintworthy_node?(last_arg)
+
+          last_name = last_arg.children.first
+
+          emit_type(*first_args, s(:kwrestarg, last_name)) unless last_name.to_s.start_with?('_')
+        end
+
+        # Is this a simple arg or arg={} ?
+        def hintworthy_node?(node)
+          n_arg?(node) ||
+            (n_optarg?(node) && node.children.last.eql?(s(:hash)))
+        end
+
         # Emit mlhs expansions
         #
         # @return [undefined]
diff --git a/meta/block.rb b/meta/block.rb
index 9627b4ec..6cafea47 100644
--- a/meta/block.rb
+++ b/meta/block.rb
@@ -19,6 +19,7 @@
 
   singleton_mutations
   mutation 'foo'
+  mutation 'foo { |a, **b| }'
   mutation 'foo { |a, b| raise }'
   mutation 'foo { |a, _b| }'
   mutation 'foo { |_a, b| }'
@@ -32,6 +33,7 @@
 
   singleton_mutations
   mutation 'foo { || }'
+  mutation 'foo { |(a, b), **c| }'
   mutation 'foo { |a, b, c| }'
   mutation 'foo { |(a, b), c| raise }'
   mutation 'foo { |(a), c| }'
diff --git a/meta/def.rb b/meta/def.rb
index e50bd6bf..8f89ce2b 100644
--- a/meta/def.rb
+++ b/meta/def.rb
@@ -5,6 +5,30 @@
   mutation 'def foo; super; end'
 end
 
+Mutest::Meta::Example.add :def do
+  source 'def foo(a); end'
+
+  mutation 'def foo; end'
+  mutation 'def foo(_a); end'
+  mutation 'def foo(**a); end'
+  mutation 'def foo(a); raise; end'
+  mutation 'def foo(a); super; end'
+end
+
+Mutest::Meta::Example.add :def do
+  source 'def foo(a = {}); end'
+
+  mutation 'def foo; end'
+  mutation 'def foo(**a); end'
+  mutation 'def foo(_a = {}); end'
+  mutation 'def foo(a); end'
+  mutation 'def foo(a = nil); end'
+  mutation 'def foo(a = self); end'
+  mutation 'def foo(a = {}); a = {}; end'
+  mutation 'def foo(a = {}); super; end'
+  mutation 'def foo(a = {}); raise; end'
+end
+
 Mutest::Meta::Example.add :def do
   source 'def foo(a, *b); nil; end'
 
@@ -106,6 +130,9 @@
   # Deletion of all arguments
   mutation 'def foo; end'
 
+  # Hash type hint
+  mutation 'def foo(a, **b); end'
+
   # Rename each argument
   mutation 'def foo(_a, b); end'
   mutation 'def foo(a, _b); end'
@@ -220,6 +247,9 @@
   # Deletion of all arguments
   mutation 'def self.foo; end'
 
+  # Hash type hint
+  mutation 'def self.foo(a, **b); end'
+
   # Rename each argument
   mutation 'def self.foo(_a, b); end'
   mutation 'def self.foo(a, _b); end'