diff --git a/requests/models.py b/requests/models.py
index 1a434740..3ec600ec 100644
--- a/requests/models.py
+++ b/requests/models.py
@@ -220,7 +220,7 @@ class Request(RequestHooksMixin):
         for (k, v) in list(hooks.items()):
             self.register_hook(event=k, hook=v)
 
-        self.method = to_native_string(method)
+        self.method = method
         self.url = url
         self.headers = headers
         self.files = files
@@ -318,8 +318,9 @@ class PreparedRequest(RequestEncodingMixin, RequestHooksMixin):
     def prepare_method(self, method):
         """Prepares the given HTTP method."""
         self.method = method
-        if self.method is not None:
-            self.method = to_native_string(self.method.upper())
+        if self.method is None:
+            raise ValueError('Request method cannot be "None"')
+        self.method = to_native_string(self.method).upper()
 
     def prepare_url(self, url, params):
         """Prepares the given HTTP URL."""
diff --git a/test_requests.py b/test_requests.py
index c377cc56..a89a7fc0 100755
--- a/test_requests.py
+++ b/test_requests.py
@@ -1738,6 +1738,16 @@ def test_prepare_unicode_url():
     assert_copy(p, p.copy())
 
 
+def test_prepare_requires_a_request_method():
+    req = Request()
+    with pytest.raises(ValueError):
+        req.prepare()
+
+    prepped = PreparedRequest()
+    with pytest.raises(ValueError):
+        prepped.prepare()
+
+
 def test_urllib3_retries(httpbin):
     from requests.packages.urllib3.util import Retry
     s = requests.Session()