diff --git a/stdlib/pp/0/pp.rbs b/stdlib/pp/0/pp.rbs
index c543439a5..c09968e17 100644
--- a/stdlib/pp/0/pp.rbs
+++ b/stdlib/pp/0/pp.rbs
@@ -59,9 +59,9 @@ class PP < PrettyPrint
   VERSION: String
 
   interface _PrettyPrint
-    def pretty_print: (untyped q) -> untyped
+    def pretty_print: (untyped q) -> void
 
-    def pretty_print_cycle: (untyped q) -> untyped
+    def pretty_print_cycle: (untyped q) -> void
 
     def is_a?: (Module) -> bool
   end
@@ -127,7 +127,7 @@ class PP < PrettyPrint
     # Object#pretty_print_cycle is used when `obj` is already printed, a.k.a the
     # object reference chain has a cycle.
     #
-    def pp: (_PrettyPrint obj) -> untyped
+    def pp: (_PrettyPrint obj) -> void
 
     # <!--
     #   rdoc-file=lib/pp.rb
@@ -203,7 +203,7 @@ class PP < PrettyPrint
     # -->
     # A present standard failsafe for pretty printing any given Object
     #
-    def pp_object: (untyped obj) -> untyped
+    def pp_object: (untyped obj) -> void
 
     # <!--
     #   rdoc-file=lib/pp.rb
@@ -211,7 +211,7 @@ class PP < PrettyPrint
     # -->
     # A pretty print for a Hash
     #
-    def pp_hash: (untyped obj) -> untyped
+    def pp_hash: (untyped obj) -> void
   end
   include PPMethods
 
@@ -220,13 +220,13 @@ class PP < PrettyPrint
   end
 
   module ObjectMixin : BasicObject
-    def pretty_print: (PP q) -> untyped
+    def pretty_print: (PP q) -> void
 
-    def pretty_print_cycle: (PP q) -> untyped
+    def pretty_print_cycle: (PP q) -> void
 
     def pretty_print_instance_variables: () -> Array[Symbol]
 
-    def pretty_print_inspect: () -> untyped
+    def pretty_print_inspect: () -> String
   end
 
   # <!--
@@ -256,7 +256,8 @@ class PP < PrettyPrint
   #
   # PP.pp returns `out`.
   #
-  def self.pp: (_PrettyPrint obj, ?_LeftShift out, ?Integer width) -> untyped
+  def self.pp: (_PrettyPrint obj) -> IO
+             | [T < _LeftShift] (_PrettyPrint obj, T out, ?Integer width) -> T
 
   # <!--
   #   rdoc-file=lib/pp.rb
@@ -266,7 +267,8 @@ class PP < PrettyPrint
   #
   # PP.singleline_pp returns `out`.
   #
-  def self.singleline_pp: (_PrettyPrint obj, ?_LeftShift out) -> untyped
+  def self.singleline_pp: (_PrettyPrint obj) -> IO
+                        | [T < _LeftShift] (_PrettyPrint obj, T out) -> T
   def self.mcall: (untyped obj, Module mod, interned meth, *untyped args) ?{ (*untyped, **untyped) -> untyped } -> untyped
 
   # <!--
diff --git a/test/stdlib/PP_test.rb b/test/stdlib/PP_test.rb
index b5f1562f6..fd0c88c43 100644
--- a/test/stdlib/PP_test.rb
+++ b/test/stdlib/PP_test.rb
@@ -12,11 +12,15 @@ def test_version
   end
 
   def test_pp
-    assert_send_type "(::PP::_PrettyPrint obj, ?::PP::_LeftShift out, ?::Integer width) -> untyped",
+    assert_send_type "(::PP::_PrettyPrint obj) -> ::IO",
+                     PP, :pp, Object.new
+    assert_send_type "(::PP::_PrettyPrint obj, ::String out) -> ::String",
                      PP, :pp, Object.new, ''.dup
+    assert_send_type "(::PP::_PrettyPrint obj, ::String out, ::Integer width) -> ::String",
+                     PP, :pp, Object.new, ''.dup, 10
 
     IO.pipe do |r, w|
-      assert_send_type "(::PP::_PrettyPrint obj, ?::PP::_LeftShift out, ?::Integer width) -> untyped",
+      assert_send_type "(::PP::_PrettyPrint obj, ::IO out) -> ::IO",
                       PP, :pp, Object.new, w
     end
   end
@@ -29,9 +33,9 @@ def test_width_for
   end
 
   def test_singleline_pp
-    assert_send_type "(::PP::_PrettyPrint obj, ?::PP::_LeftShift out) -> untyped",
+    assert_send_type "(::PP::_PrettyPrint obj) -> ::IO",
                      PP, :singleline_pp, Object.new
-    assert_send_type "(::PP::_PrettyPrint obj, ?::PP::_LeftShift out) -> untyped",
+    assert_send_type "(::PP::_PrettyPrint obj, ::String out) -> ::String",
                      PP, :singleline_pp, Object.new, ''.dup
   end
 
@@ -72,7 +76,7 @@ def test_pop_inspect_key
   end
 
   def test_pp
-    assert_send_type "(::PP::_PrettyPrint obj) -> untyped",
+    assert_send_type "(::PP::_PrettyPrint obj) -> void",
                      PP.new, :pp, Object.new
   end
 
@@ -101,12 +105,12 @@ def test_seplist
   end
 
   def test_pp_object
-    assert_send_type "(untyped obj) -> untyped",
+    assert_send_type "(untyped obj) -> void",
                      PP.new, :pp_object, Object.new
   end
 
   def test_pp_hash
-    assert_send_type "(untyped obj) -> untyped",
+    assert_send_type "(untyped obj) -> void",
                      PP.new, :pp_hash, {}
   end
 
@@ -123,12 +127,12 @@ class PP::ObjectMixinTest < Test::Unit::TestCase
   testing "::PP::ObjectMixin"
 
   def test_pretty_print
-    assert_send_type "(PP q) -> untyped",
+    assert_send_type "(PP q) -> void",
                      Object.new, :pretty_print, PP.new
   end
 
   def test_pretty_print_cycle
-    assert_send_type "(PP q) -> untyped",
+    assert_send_type "(PP q) -> void",
                      Object.new, :pretty_print_cycle, PP.new
   end
 
@@ -143,7 +147,7 @@ def pretty_print(q)
         'ok'
       end
     end
-    assert_send_type "() -> untyped",
+    assert_send_type "() -> ::String",
                      has_pretty_print.new, :pretty_print_inspect
   end
 end