diff --git a/.travis.yml b/.travis.yml
index 3e8b48828..c601955d7 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -26,6 +26,8 @@ matrix:
       env: TOXENV=py36 BDIST=1 WHEEL=1
     - python: 3.6
       env: TOXENV=individual_coverage
+    - python: "3.7-dev"
+      env: TOXENV=py37
     - language: node_js
       node_js: "node"
       before_install:
diff --git a/test/mitmproxy/net/http/test_url.py b/test/mitmproxy/net/http/test_url.py
index c9f61fafd..ecf8e8969 100644
--- a/test/mitmproxy/net/http/test_url.py
+++ b/test/mitmproxy/net/http/test_url.py
@@ -63,17 +63,21 @@ def test_unparse():
     assert url.unparse("https", "foo.com", 443, "") == "https://foo.com"
 
 
-surrogates = bytes(range(256)).decode("utf8", "surrogateescape")
+# We ignore the byte 126: '~' because of an incompatibility in Python 3.6 and 3.7
+# In 3.6 it is escaped as %7E
+# In 3.7 it stays as ASCII character '~'
+# https://bugs.python.org/issue16285
+surrogates = (bytes(range(0, 126)) + bytes(range(127, 256))).decode("utf8", "surrogateescape")
 
 surrogates_quoted = (
     '%00%01%02%03%04%05%06%07%08%09%0A%0B%0C%0D%0E%0F'
     '%10%11%12%13%14%15%16%17%18%19%1A%1B%1C%1D%1E%1F'
     '%20%21%22%23%24%25%26%27%28%29%2A%2B%2C-./'
-    '0123456789%3A%3B%3C%3D%3E%3F'
-    '%40ABCDEFGHIJKLMNO'
-    'PQRSTUVWXYZ%5B%5C%5D%5E_'
-    '%60abcdefghijklmno'
-    'pqrstuvwxyz%7B%7C%7D%7E%7F'
+    '0123456789%3A%3B%3C%3D%3E%3F%40'
+    'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
+    '%5B%5C%5D%5E_%60'
+    'abcdefghijklmnopqrstuvwxyz'
+    '%7B%7C%7D%7F'  # 7E or ~ is excluded!
     '%80%81%82%83%84%85%86%87%88%89%8A%8B%8C%8D%8E%8F'
     '%90%91%92%93%94%95%96%97%98%99%9A%9B%9C%9D%9E%9F'
     '%A0%A1%A2%A3%A4%A5%A6%A7%A8%A9%AA%AB%AC%AD%AE%AF'
diff --git a/tox.ini b/tox.ini
index 475f19513..a9054e5b2 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = py36, lint
+envlist = py36, py37, lint
 skipsdist = True
 toxworkdir={env:TOX_WORK_DIR:.tox}