diff --git a/Lib/cgi.py b/Lib/cgi.py
index c22c71b3878516..54f2812f5c414c 100755
--- a/Lib/cgi.py
+++ b/Lib/cgi.py
@@ -663,11 +663,9 @@ def read_multi(self, environ, keep_blank_values, strict_parsing):
 
     def read_single(self):
         """Internal: read an atomic part."""
+        self.read_lines()
         if self.length >= 0:
-            self.read_binary()
             self.skip_lines()
-        else:
-            self.read_lines()
         self.file.seek(0)
 
     bufsize = 8*1024            # I/O buffering size for copy to file
diff --git a/Lib/test/test_cgi.py b/Lib/test/test_cgi.py
index ab8677199f32e7..9080ac6f96d8e2 100644
--- a/Lib/test/test_cgi.py
+++ b/Lib/test/test_cgi.py
@@ -352,6 +352,18 @@ def test_fieldstorage_part_content_length(self):
         self.assertEqual(fs.list[0].name, 'submit-name')
         self.assertEqual(fs.list[0].value, 'Larry')
 
+    def test_content_length_no_content_disposition(self):
+        body = b'{"test":123}'
+        env = {
+            'CONTENT_LENGTH': len(body),
+            'REQUEST_METHOD': 'POST',
+            'CONTENT_TYPE': 'application/json',
+            'wsgi.input': BytesIO(body),
+        }
+
+        form = cgi.FieldStorage(fp=env['wsgi.input'], environ=env)
+        self.assertEqual(form.file.read(), body.decode(form.encoding))
+
     def test_field_storage_multipart_no_content_length(self):
         fp = BytesIO(b"""--MyBoundary
 Content-Disposition: form-data; name="my-arg"; filename="foo"
diff --git a/Misc/NEWS.d/next/Library/2018-11-28-17-47-47.bpo-27777.AKUxDR.rst b/Misc/NEWS.d/next/Library/2018-11-28-17-47-47.bpo-27777.AKUxDR.rst
new file mode 100644
index 00000000000000..c967372ae7a9c8
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2018-11-28-17-47-47.bpo-27777.AKUxDR.rst
@@ -0,0 +1,2 @@
+Fixes a bug in :mod:`cgi` when a request has a "Content-Length" header but
+without "Content-Disposition" headers.