diff --git a/httpie/input.py b/httpie/input.py
index ff0bf034..88bc3c87 100644
--- a/httpie/input.py
+++ b/httpie/input.py
@@ -21,6 +21,10 @@ from httpie.sessions import VALID_SESSION_NAME_PATTERN
 from httpie.utils import load_json_preserve_order
 
 
+# ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
+# <http://tools.ietf.org/html/rfc3986#section-3.1>
+URL_SCHEME_RE = re.compile(r'^[a-z][a-z0-9.+-]*://', re.IGNORECASE)
+
 HTTP_POST = 'POST'
 HTTP_GET = 'GET'
 HTTP = 'http://'
@@ -132,7 +136,7 @@ class Parser(ArgumentParser):
         self._parse_items()
         if not self.args.ignore_stdin and not env.stdin_isatty:
             self._body_from_file(self.env.stdin)
-        if not (self.args.url.startswith((HTTP, HTTPS))):
+        if not URL_SCHEME_RE.match(self.args.url):
             scheme = HTTP
 
             # See if we're using curl style shorthand for localhost (:3000/foo)
diff --git a/tests/test_cli.py b/tests/test_cli.py
index f5754edc..73f68f71 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -2,9 +2,9 @@
 import json
 # noinspection PyCompatibility
 import argparse
-import os
 
 import pytest
+from requests.exceptions import InvalidSchema
 
 from httpie import input
 from httpie.input import KeyValue, KeyValueArgType, DataDict
@@ -321,3 +321,12 @@ class TestIgnoreStdin:
                  error_exit_ok=True)
         assert r.exit_status == ExitStatus.ERROR
         assert 'because --ignore-stdin' in r.stderr
+
+
+class TestSchemes:
+
+    def test_custom_scheme(self):
+        # InvalidSchema is expected because HTTPie
+        # shouldn't touch a formally valid scheme.
+        with pytest.raises(InvalidSchema):
+            http('foo+bar-BAZ.123://bah')