diff --git a/lib/irb/ruby-lex.rb b/lib/irb/ruby-lex.rb
index 006fc191b..b41126f98 100644
--- a/lib/irb/ruby-lex.rb
+++ b/lib/irb/ruby-lex.rb
@@ -456,6 +456,34 @@ def take_corresponding_syntax_to_kw_do(tokens, index)
     syntax_of_do
   end
 
+  def is_the_in_correspond_to_a_for(tokens, index)
+    syntax_of_in = nil
+    # Finding a syntax correnponding to "do".
+    index.downto(0) do |i|
+      tk = tokens[i]
+      # In "continue", the token isn't the corresponding syntax to "do".
+      non_sp_index = tokens[0..(i - 1)].rindex{ |t| t[1] != :on_sp }
+      first_in_fomula = false
+      if non_sp_index.nil?
+        first_in_fomula = true
+      elsif [:on_ignored_nl, :on_nl, :on_comment].include?(tokens[non_sp_index][1])
+        first_in_fomula = true
+      end
+      if tk[1] == :on_kw && tk[2] == 'for'
+        # A loop syntax in front of "do" found.
+        #
+        #   while cond do # also "until" or "for"
+        #   end
+        #
+        # This "do" doesn't increment indent because the loop syntax already
+        # incremented.
+        syntax_of_in = :for
+      end
+      break if first_in_fomula
+    end
+    syntax_of_in
+  end
+
   def check_newline_depth_difference
     depth_difference = 0
     open_brace_on_line = 0
@@ -511,8 +539,12 @@ def check_newline_depth_difference
           unless t[3].allbits?(Ripper::EXPR_LABEL)
             depth_difference += 1
           end
-        when 'else', 'elsif', 'ensure', 'when', 'in'
+        when 'else', 'elsif', 'ensure', 'when'
           depth_difference += 1
+        when 'in'
+          unless is_the_in_correspond_to_a_for(@tokens, index)
+            depth_difference += 1
+          end
         when 'end'
           depth_difference -= 1
         end
diff --git a/test/irb/test_ruby_lex.rb b/test/irb/test_ruby_lex.rb
index ed4944afc..7a001116b 100644
--- a/test/irb/test_ruby_lex.rb
+++ b/test/irb/test_ruby_lex.rb
@@ -333,6 +333,38 @@ def test_corresponding_syntax_to_keyword_do
       end
     end
 
+    def test_corresponding_syntax_to_keyword_for
+      input_with_correct_indents = [
+        Row.new(%q(for i in [1]), nil, 2, 1),
+        Row.new(%q(  puts i), nil, 2, 1),
+        Row.new(%q(end), 0, 0, 0),
+      ]
+
+      lines = []
+      input_with_correct_indents.each do |row|
+        lines << row.content
+        assert_indenting(lines, row.current_line_spaces, false)
+        assert_indenting(lines, row.new_line_spaces, true)
+        assert_nesting_level(lines, row.nesting_level)
+      end
+    end
+
+    def test_corresponding_syntax_to_keyword_for_with_do
+      input_with_correct_indents = [
+        Row.new(%q(for i in [1] do), nil, 2, 1),
+        Row.new(%q(  puts i), nil, 2, 1),
+        Row.new(%q(end), 0, 0, 0),
+      ]
+
+      lines = []
+      input_with_correct_indents.each do |row|
+        lines << row.content
+        assert_indenting(lines, row.current_line_spaces, false)
+        assert_indenting(lines, row.new_line_spaces, true)
+        assert_nesting_level(lines, row.nesting_level)
+      end
+    end
+
     def test_heredoc_with_indent
       input_with_correct_indents = [
         Row.new(%q(<<~Q), nil, 0, 0),