diff --git a/scrapy/downloadermiddlewares/httpproxy.py b/scrapy/downloadermiddlewares/httpproxy.py
index 04da11311..d2665b655 100644
--- a/scrapy/downloadermiddlewares/httpproxy.py
+++ b/scrapy/downloadermiddlewares/httpproxy.py
@@ -13,7 +13,12 @@ class HttpProxyMiddleware:
         self.auth_encoding = auth_encoding
         self.proxies = {}
         for type_, url in getproxies().items():
-            self.proxies[type_] = self._get_proxy(url, type_)
+            try:
+                self.proxies[type_] = self._get_proxy(url, type_)
+            # some values such as '/var/run/docker.sock' can't be parsed
+            # by _parse_proxy and as such should be skipped
+            except ValueError:
+                continue
 
     @classmethod
     def from_crawler(cls, crawler):
diff --git a/tests/test_downloadermiddleware_httpproxy.py b/tests/test_downloadermiddleware_httpproxy.py
index 351631eb8..81d6cc335 100644
--- a/tests/test_downloadermiddleware_httpproxy.py
+++ b/tests/test_downloadermiddleware_httpproxy.py
@@ -123,7 +123,11 @@ class TestHttpProxyMiddleware(TestCase):
 
     def test_no_proxy(self):
         os.environ['http_proxy'] = 'https://proxy.for.http:3128'
+        os.environ['no_proxy'] = '/var/run/docker.sock'
         mw = HttpProxyMiddleware()
+        # '/var/run/docker.sock' may be used by the user for
+        # no_proxy value but is not parseable and should be skipped
+        assert 'no' not in mw.proxies
 
         os.environ['no_proxy'] = '*'
         req = Request('http://noproxy.com')