diff --git a/CHANGES.rst b/CHANGES.rst
index fe9870aa..64892ae9 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -12,8 +12,12 @@ Unreleased
 -   :meth:`flask.RequestContext.copy` includes the current session
     object in the request context copy. This prevents ``flask.session`` 
     pointing to an out-of-date object. (`#2935`)
+-   Using built-in RequestContext, unprintable Unicode characters in Host
+    header will result in a HTTP 400 response and not HTTP 500 as previously.
+    (`#2994`)
 
 .. _#2935: https://github.com/pallets/flask/issues/2935
+.. _#2994: https://github.com/pallets/flask/pull/2994
 
 
 Version 1.0.3
diff --git a/flask/ctx.py b/flask/ctx.py
index e41adbd2..f8cdb60b 100644
--- a/flask/ctx.py
+++ b/flask/ctx.py
@@ -282,7 +282,11 @@ class RequestContext(object):
         if request is None:
             request = app.request_class(environ)
         self.request = request
-        self.url_adapter = app.create_url_adapter(self.request)
+        self.url_adapter = None
+        try:
+            self.url_adapter = app.create_url_adapter(self.request)
+        except HTTPException as e:
+            self.request.routing_exception = e
         self.flashes = None
         self.session = session
 
@@ -305,7 +309,8 @@ class RequestContext(object):
         # functions.
         self._after_request_functions = []
 
-        self.match_request()
+        if self.url_adapter is not None:
+            self.match_request()
 
     def _get_g(self):
         return _app_ctx_stack.top.g
diff --git a/tests/test_reqctx.py b/tests/test_reqctx.py
index d8ef4970..6cb9c37d 100644
--- a/tests/test_reqctx.py
+++ b/tests/test_reqctx.py
@@ -229,3 +229,57 @@ def test_session_error_pops_context():
     assert response.status_code == 500
     assert not flask.request
     assert not flask.current_app
+
+
+def test_bad_environ_raises_bad_request():
+    app = flask.Flask(__name__)
+
+    # We cannot use app.test_client() for the Unicode-rich Host header,
+    # because werkzeug enforces latin1 on Python 2.
+    # However it works when actually passed to the server.
+
+    from flask.testing import make_test_environ_builder
+    builder = make_test_environ_builder(app)
+    environ = builder.get_environ()
+
+    # use a non-printable character in the Host - this is key to this test
+    environ['HTTP_HOST'] = u'\x8a'
+
+    with app.request_context(environ):
+        response = app.full_dispatch_request()
+    assert response.status_code == 400
+
+
+def test_environ_for_valid_idna_completes():
+    app = flask.Flask(__name__)
+
+    @app.route('/')
+    def index():
+        return 'Hello World!'
+
+    # We cannot use app.test_client() for the Unicode-rich Host header,
+    # because werkzeug enforces latin1 on Python 2.
+    # However it works when actually passed to the server.
+
+    from flask.testing import make_test_environ_builder
+    builder = make_test_environ_builder(app)
+    environ = builder.get_environ()
+
+    # these characters are all IDNA-compatible
+    environ['HTTP_HOST'] = u'ąśźäüжŠßя.com'
+
+    with app.request_context(environ):
+        response = app.full_dispatch_request()
+
+    assert response.status_code == 200
+
+
+def test_normal_environ_completes():
+    app = flask.Flask(__name__)
+
+    @app.route('/')
+    def index():
+        return 'Hello World!'
+
+    response = app.test_client().get('/', headers={'host': 'xn--on-0ia.com'})
+    assert response.status_code == 200