diff --git a/lib/rbs.rb b/lib/rbs.rb
index 0559fa422..a9bbdc839 100644
--- a/lib/rbs.rb
+++ b/lib/rbs.rb
@@ -39,6 +39,7 @@
 require "rbs/prototype/rbi"
 require "rbs/prototype/rb"
 require "rbs/prototype/runtime"
+require "rbs/prototype/node_usage"
 require "rbs/type_name_resolver"
 require "rbs/environment_walker"
 require "rbs/vendorer"
diff --git a/lib/rbs/prototype/helpers.rb b/lib/rbs/prototype/helpers.rb
index 10baa0679..1c36ff18e 100644
--- a/lib/rbs/prototype/helpers.rb
+++ b/lib/rbs/prototype/helpers.rb
@@ -7,27 +7,43 @@ module Helpers
 
       def block_from_body(node)
         _, args_node, body_node = node.children
+        _pre_num, _pre_init, _opt, _first_post, _post_num, _post_init, _rest, _kw, _kwrest, block_var = args_from_node(args_node)
 
-        _pre_num, _pre_init, _opt, _first_post, _post_num, _post_init, _rest, _kw, _kwrest, block = args_from_node(args_node)
+        # @type var body_node: node?
+        if body_node
+          yields = any_node?(body_node) {|n| n.type == :YIELD }
+        end
+
+        if yields || block_var
+          required = true
+
+          if body_node
+            if any_node?(body_node) {|n| n.type == :FCALL && n.children[0] == :block_given? && !n.children[1] }
+              required = false
+            end
+          end
+
+          if _rest == :* && block_var == :&
+            # ... is given
+            required = false
+          end
 
-        method_block = nil
+          if block_var
+            if body_node
+              usage = NodeUsage.new(body_node)
+              if usage.each_conditional_node.any? {|n| n.type == :LVAR && n.children[0] == block_var }
+                required = false
+              end
+            end
+          end
 
-        if block
           method_block = Types::Block.new(
-            required: false,
+            required: required,
             type: Types::Function.empty(untyped),
             self_type: nil
           )
-        end
-
-        if body_node
-          if (yields = any_node?(body_node) {|n| n.type == :YIELD })
-            method_block = Types::Block.new(
-              required: true,
-              type: Types::Function.empty(untyped),
-              self_type: nil
-            )
 
+          if yields
             yields.each do |yield_node|
               array_content = yield_node.children[0]&.children&.compact || []
 
diff --git a/lib/rbs/prototype/node_usage.rb b/lib/rbs/prototype/node_usage.rb
new file mode 100644
index 000000000..2c5f07e0b
--- /dev/null
+++ b/lib/rbs/prototype/node_usage.rb
@@ -0,0 +1,99 @@
+# frozen_string_literal: true
+
+module RBS
+  module Prototype
+    class NodeUsage
+      include Helpers
+
+      attr_reader :conditional_nodes
+
+      def initialize(node)
+        @node = node
+        @conditional_nodes = Set[].compare_by_identity
+
+        calculate(node, conditional: false)
+      end
+
+      def each_conditional_node(&block)
+        if block
+          conditional_nodes.each(&block)
+        else
+          conditional_nodes.each
+        end
+      end
+
+      def calculate(node, conditional:)
+        if conditional
+          conditional_nodes << node
+        end
+
+        case node.type
+        when :IF, :UNLESS
+          cond_node, true_node, false_node = node.children
+          calculate(cond_node, conditional: true)
+          calculate(true_node, conditional: conditional) if true_node
+          calculate(false_node, conditional: conditional) if false_node
+        when :AND, :OR
+          left, right = node.children
+          calculate(left, conditional: true)
+          calculate(right, conditional: conditional)
+        when :QCALL
+          receiver, _, args = node.children
+          calculate(receiver, conditional: true)
+          calculate(args, conditional: false) if args
+        when :WHILE
+          cond, body = node.children
+          calculate(cond, conditional: true)
+          calculate(body, conditional: false) if body
+        when :OP_ASGN_OR, :OP_ASGN_AND
+          var, _, asgn = node.children
+          calculate(var, conditional: true)
+          calculate(asgn, conditional: conditional)
+        when :LASGN, :IASGN, :GASGN
+          _, lhs = node.children
+          calculate(lhs, conditional: conditional) if lhs
+        when :MASGN
+          lhs, _ = node.children
+          calculate(lhs, conditional: conditional)
+        when :CDECL
+          if node.children.size == 2
+            _, lhs = node.children
+            calculate(lhs, conditional: conditional)
+          else
+            const, _, lhs = node.children
+            calculate(const, conditional: false)
+            calculate(lhs, conditional: conditional)
+          end
+        when :SCOPE
+          _, _, body = node.children
+          calculate(body, conditional: conditional)
+        when :CASE2
+          _, *branches = node.children
+          branches.each do |branch|
+            if branch.type == :WHEN
+              list, body = branch.children
+              list.children.each do |child|
+                if child
+                  calculate(child, conditional: true)
+                end
+              end
+              calculate(body, conditional: conditional)
+            else
+              calculate(branch, conditional: conditional)
+            end
+          end
+        when :BLOCK
+          *nodes, last = node.children
+          nodes.each do |no|
+            calculate(no, conditional: false)
+          end
+          calculate(last, conditional: conditional) if last
+        else
+          each_child(node) do |child|
+            calculate(child, conditional: false)
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/sig/prototype/node_usage.rbs b/sig/prototype/node_usage.rbs
new file mode 100644
index 000000000..6a72f8346
--- /dev/null
+++ b/sig/prototype/node_usage.rbs
@@ -0,0 +1,20 @@
+module RBS
+  module Prototype
+    class NodeUsage
+      include Helpers
+      
+      type node = RubyVM::AbstractSyntaxTree::Node
+
+      attr_reader node: node
+
+      attr_reader conditional_nodes: Set[node]
+
+      def initialize: (node) -> void
+
+      def calculate: (node, conditional: bool) -> void
+
+      def each_conditional_node: () { (node) -> void } -> void
+                               | () -> Enumerator[node, void]
+    end
+  end
+end
diff --git a/test/rbs/node_usage_test.rb b/test/rbs/node_usage_test.rb
new file mode 100644
index 000000000..5ded3b572
--- /dev/null
+++ b/test/rbs/node_usage_test.rb
@@ -0,0 +1,47 @@
+require "test_helper"
+
+class RBS::NodeUsageTest < Test::Unit::TestCase
+  include RBS::Prototype
+
+  def parse(string)
+    RubyVM::AbstractSyntaxTree.parse(string)
+  end
+
+  def test_conditional
+    usage = NodeUsage.new(parse(<<~RB))
+      if block
+        yield
+      end
+
+      foo && bar || baz
+
+      1&.+(2)
+
+      begin
+        bar
+      end while baz
+
+      a ||= b
+      a += 123
+
+      x = 1
+      @y = 2
+      Z = 3
+      Z::Z1 = 4
+
+      x, y, z = foo
+
+      puts unless foo
+
+      case
+      when foo
+      else
+        hello
+      end
+
+      [
+        (foo(); bar; baz)
+      ]
+    RB
+  end
+end
diff --git a/test/rbs/rb_prototype_test.rb b/test/rbs/rb_prototype_test.rb
index abbb575dc..87d119a3f 100644
--- a/test/rbs/rb_prototype_test.rb
+++ b/test/rbs/rb_prototype_test.rb
@@ -62,7 +62,7 @@ def kw_req(a:) end
 
     assert_write parser.decls, <<-EOF
 class Hello
-  def hello: (untyped a, ?::Integer b, *untyped c, untyped d, e: untyped, ?f: ::Integer, **untyped g) ?{ () -> untyped } -> nil
+  def hello: (untyped a, ?::Integer b, *untyped c, untyped d, e: untyped, ?f: ::Integer, **untyped g) { () -> untyped } -> nil
 
   def self.world: () { (untyped, untyped, untyped, x: untyped, y: untyped) -> untyped } -> untyped
 
@@ -233,6 +233,38 @@ def when_last_is_nil: () -> nil
     EOF
   end
 
+  def test_defs_return_type_with_block_optional
+      parser = RB.new
+
+      rb = <<~'EOR'
+        class Hello
+          def with_optional_block1
+            # `block_given?` call makes the block optional
+            if block_given?
+              yield 1
+            end
+          end
+
+          def with_optional_block2(&block)
+            # testing block var makes the block optional
+            if block
+              yield 1
+            end
+          end
+        end
+      EOR
+
+      parser.parse(rb)
+
+      assert_write parser.decls, <<~EOF
+        class Hello
+          def with_optional_block1: () ?{ (untyped) -> untyped } -> (untyped | nil)
+
+          def with_optional_block2: () ?{ (untyped) -> untyped } -> (untyped | nil)
+        end
+      EOF
+    end
+
   def test_defs_return_type_with_if
     parser = RB.new