diff --git a/lib/cgi/core.rb b/lib/cgi/core.rb
index b5c3a1e..69373cb 100644
--- a/lib/cgi/core.rb
+++ b/lib/cgi/core.rb
@@ -838,13 +838,16 @@ def read_from_cmdline
     # Handles multipart forms (in particular, forms that involve file uploads).
     # Reads query parameters in the @params field, and cookies into @cookies.
     def initialize_query()
+      content_length = env_table['CONTENT_LENGTH']
+      content_length = nil if content_length == ''
       if ("POST" == env_table['REQUEST_METHOD']) and
         %r|\Amultipart/form-data.*boundary=\"?([^\";,]+)\"?| =~ env_table['CONTENT_TYPE']
         current_max_multipart_length = @max_multipart_length.respond_to?(:call) ? @max_multipart_length.call : @max_multipart_length
         raise StandardError.new("too large multipart data.") if env_table['CONTENT_LENGTH'].to_i > current_max_multipart_length
+        raise StandardError.new("no content length for multipart data.") if content_length.nil?
         boundary = $1.dup
         @multipart = true
-        @params = read_multipart(boundary, Integer(env_table['CONTENT_LENGTH']))
+        @params = read_multipart(boundary, Integer(content_length))
       else
         @multipart = false
         @params = CGI.parse(
@@ -857,7 +860,11 @@ def initialize_query()
                       end
                     when "POST"
                       stdinput.binmode if defined? stdinput.binmode
-                      stdinput.read(Integer(env_table['CONTENT_LENGTH'])) or ''
+                      if content_length.nil?
+                        stdinput.read or ''
+                      else
+                        stdinput.read(Integer(content_length)) or ''
+                      end
                     else
                       read_from_cmdline
                     end.dup.force_encoding(@accept_charset)
diff --git a/test/cgi/test_cgi_core.rb b/test/cgi/test_cgi_core.rb
index f7adb7e..b805c31 100644
--- a/test/cgi/test_cgi_core.rb
+++ b/test/cgi/test_cgi_core.rb
@@ -92,6 +92,33 @@ def test_cgi_core_params_POST
     $stdin = STDIN
   end
 
+  def test_cgi_core_params_POST_without_content_length
+    update_env(
+      'REQUEST_METHOD'  => 'POST',
+      'CONTENT_TYPE'    => 'application/x-www-form-urlencoded',
+    )
+    $stdin = StringIO.new
+    cgi = nil
+    assert_nothing_raised { cgi = CGI.new }
+    assert_equal({}, cgi.params)
+  ensure
+    $stdin = STDIN
+  end
+
+  def test_cgi_core_params_POST_empty_content_length
+    update_env(
+      'REQUEST_METHOD'  => 'POST',
+      'CONTENT_TYPE'    => 'application/x-www-form-urlencoded',
+      'CONTENT_LENGTH'  => '',
+    )
+    $stdin = StringIO.new
+    cgi = nil
+    assert_nothing_raised { cgi = CGI.new }
+    assert_equal({}, cgi.params)
+  ensure
+    $stdin = STDIN
+  end
+
   def test_cgi_core_params_encoding_check
     query_str = 'str=%BE%BE%B9%BE'
     update_env(