diff --git a/lib/webrick/httputils.rb b/lib/webrick/httputils.rb
index e2c2a40..40ba32f 100644
--- a/lib/webrick/httputils.rb
+++ b/lib/webrick/httputils.rb
@@ -176,10 +176,19 @@ def parse_header(raw)
         when /^([A-Za-z0-9!\#$%&'*+\-.^_`|~]+):([^\r\n\0]*?)\r\n\z/om
           field, value = $1, $2
           field.downcase!
-          header[field] = HEADER_CLASSES[field].new unless header.has_key?(field)
+          if header.has_key?(field)
+            if field == "transfer-encoding"
+              raise HTTPStatus::BadRequest, "duplicate 'transfer-encoding' header."
+            end
+          else
+            header[field] = HEADER_CLASSES[field].new
+          end
           header[field] << value
         when /^[ \t]+([^\r\n\0]*?)\r\n/om
-          unless field
+          case field
+          when "transfer-encoding"
+            raise HTTPStatus::BadRequest, "'transfer-encoding' header with obsolete line folding."
+          when nil
             raise HTTPStatus::BadRequest, "bad header '#{line}'."
           end
           value = line
diff --git a/test/webrick/test_httprequest.rb b/test/webrick/test_httprequest.rb
index 3d02573..655df11 100644
--- a/test/webrick/test_httprequest.rb
+++ b/test/webrick/test_httprequest.rb
@@ -237,6 +237,36 @@ def test_content_length_and_transfer_encoding_headers_smuggling
     }
   end
 
+  def test_multiple_transfer_encoding_headers
+    msg = <<~HTTP.gsub("\n", "\r\n")
+      POST /user HTTP/1.1
+      Transfer-Encoding: chunked
+      Transfer-Encoding: identity
+
+      0
+
+    HTTP
+    req = WEBrick::HTTPRequest.new(WEBrick::Config::HTTP)
+    assert_raise(WEBrick::HTTPStatus::BadRequest){
+      req.parse(StringIO.new(msg))
+    }
+  end
+
+  def test_transfer_encoding_header_with_obs
+    msg = <<~HTTP.gsub("\n", "\r\n")
+      POST /user HTTP/1.1
+      Transfer-Encoding: chunked
+       identity
+
+      0
+
+    HTTP
+    req = WEBrick::HTTPRequest.new(WEBrick::Config::HTTP)
+    assert_raise(WEBrick::HTTPStatus::BadRequest){
+      req.parse(StringIO.new(msg))
+    }
+  end
+
   def test_parse_headers
     msg = <<~HTTP.gsub("\n", "\r\n")
       GET /path HTTP/1.1