diff --git a/ext/ripper/lib/ripper/lexer.rb b/ext/ripper/lib/ripper/lexer.rb
index cff38c617d..06db264497 100644
--- a/ext/ripper/lib/ripper/lexer.rb
+++ b/ext/ripper/lib/ripper/lexer.rb
@@ -130,6 +130,7 @@ class Ripper
       @buf = []
       @stack = []
       super()
+      @buf = @stack.pop unless @stack.empty?
       if raise_errors and !@errors.empty?
         raise SyntaxError, @errors.map(&:message).join(' ;')
       end
diff --git a/test/ripper/test_lexer.rb b/test/ripper/test_lexer.rb
index f8e751da53..3eaeb8fefa 100644
--- a/test/ripper/test_lexer.rb
+++ b/test/ripper/test_lexer.rb
@@ -90,6 +90,16 @@ class TestRipper::Lexer < Test::Unit::TestCase
     assert_equal expect, Ripper.lex(src).map {|e| e[1]}
   end
 
+  def test_stack_at_on_heredoc_beg
+    src = "a <<b"
+    expect = %I[
+      on_ident
+      on_sp
+      on_heredoc_beg
+    ]
+    assert_equal expect, Ripper.lex(src).map {|e| e[1]}
+  end
+
   def test_slice
     assert_equal "string\#{nil}\n",
       Ripper.slice(%(<<HERE\nstring\#{nil}\nHERE), "heredoc_beg .*? nl $(.*?) heredoc_end", 1)
diff --git a/version.h b/version.h
index 8b5a3425dd..10d69c4c78 100644
--- a/version.h
+++ b/version.h
@@ -12,7 +12,7 @@
 # define RUBY_VERSION_MINOR RUBY_API_VERSION_MINOR
 #define RUBY_VERSION_TEENY 0
 #define RUBY_RELEASE_DATE RUBY_RELEASE_YEAR_STR"-"RUBY_RELEASE_MONTH_STR"-"RUBY_RELEASE_DAY_STR
-#define RUBY_PATCHLEVEL 22
+#define RUBY_PATCHLEVEL 23
 
 #define RUBY_RELEASE_YEAR 2021
 #define RUBY_RELEASE_MONTH 2