diff --git a/scrapy/utils/url.py b/scrapy/utils/url.py
index c9abb12d5..c29ed4461 100644
--- a/scrapy/utils/url.py
+++ b/scrapy/utils/url.py
@@ -85,11 +85,9 @@ def add_http_if_no_scheme(url):
 
 
 def guess_scheme(url):
-    """Add an URL scheme if missing: file:// for filepath-like input or http:// otherwise."""
-    parts = urlparse(url)
-    if parts.scheme:
-        return url
-    # Note: this does not match Windows filepath
+    """Add an URL scheme if missing: file:// for filepath-like input or
+    http:// otherwise."""
+    # POSIX path
     if re.match(r'''^                   # start with...
                     (
                         \.              # ...a single dot,
@@ -99,7 +97,10 @@ def guess_scheme(url):
                     )?      # optional match of ".", ".." or ".blabla"
                     /       # at least one "/" for a file path,
                     .       # and something after the "/"
-                    ''', parts.path, flags=re.VERBOSE):
+                    ''', url, flags=re.VERBOSE):
+        return any_to_uri(url)
+    # Windows drive-letter path
+    elif re.match(r'''^[a-z]:\\''', url, flags=re.IGNORECASE):
         return any_to_uri(url)
     else:
         return add_http_if_no_scheme(url)
diff --git a/tests/test_command_shell.py b/tests/test_command_shell.py
index d664b6ade..acf8e9f71 100644
--- a/tests/test_command_shell.py
+++ b/tests/test_command_shell.py
@@ -94,7 +94,7 @@ class ShellTest(ProcessTest, SiteTest, unittest.TestCase):
 
     @defer.inlineCallbacks
     def test_local_file(self):
-        filepath = join(tests_datadir, 'test_site/index.html')
+        filepath = join(tests_datadir, 'test_site', 'index.html')
         _, out, _ = yield self.execute([filepath, '-c', 'item'])
         assert b'{}' in out