diff --git a/CHANGES.txt b/CHANGES.txt
index c7f32ea4..5966bf8c 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -4,6 +4,13 @@ Unreleased
 Bugfix
 ~~~~~~
 
+- A non-ASCII ``url_prefix`` configuration value is now converted to the same
+  "UTF-8 bytes decoded as latin-1" representation WSGI's PATH_INFO/SCRIPT_NAME
+  use for the actual request path, so it can now correctly match incoming
+  requests. Previously, a non-ASCII url_prefix could never match any request
+  path at all. See
+  https://github.com/Pylons/waitress/issues/492
+
 - Renamed the HTTP header "Trailers" to "Trailer" to fix a typo and comply with
   the correct header name as specified in RFC 7230.
 
diff --git a/src/waitress/adjustments.py b/src/waitress/adjustments.py
index 8b26eb87..65a84a2b 100644
--- a/src/waitress/adjustments.py
+++ b/src/waitress/adjustments.py
@@ -75,6 +75,17 @@ def slash_fixed_str(s):
         # always have a leading slash, replace any number of leading slashes
         # with a single slash, and strip any trailing slashes
         s = "/" + s.lstrip("/").rstrip("/")
+        # Per PEP 3333, WSGI's PATH_INFO/SCRIPT_NAME are represented as
+        # "native strings" holding raw request bytes decoded as latin-1
+        # (i.e. each byte becomes the code point of the same value),
+        # regardless of the request's actual encoding. The configured
+        # url_prefix, in contrast, is an ordinary Unicode string as the
+        # user wrote it. Encoding it the same way here (UTF-8 bytes,
+        # then decoded as latin-1) ensures comparisons against the
+        # request path (see HTTPTask.execute()) use the same
+        # convention on both sides, so a non-ASCII url_prefix can
+        # actually match. See GH #492.
+        s = s.encode("utf-8").decode("latin-1")
     return s
 
 
diff --git a/tests/test_adjustments.py b/tests/test_adjustments.py
index 86bf5ded..379c7953 100644
--- a/tests/test_adjustments.py
+++ b/tests/test_adjustments.py
@@ -174,6 +174,29 @@ def test_goodvars(self):
         # localhost...
         self.assertTupleEqual(("127.0.0.1", 8080), bind_pairs[0])
 
+    def test_url_prefix_non_ascii_matches_wsgi_encoded_path(self):
+        """
+        Regression test for
+        https://github.com/Pylons/waitress/issues/492
+
+        A non-ASCII url_prefix must be converted to the same
+        "utf8-as-latin1" representation WSGI's PATH_INFO/SCRIPT_NAME
+        use for the actual request path (see HTTPTask.execute() in
+        task.py), or a non-ASCII url_prefix can never match an
+        incoming request's path.
+        """
+        inst = self._makeOne(url_prefix="/日本語")
+
+        # What the request path would actually look like once the raw
+        # UTF-8 bytes sent by a client are decoded as latin-1, per
+        # PEP 3333's WSGI string convention.
+        expected = "/日本語".encode("utf-8").decode("latin-1")
+        self.assertEqual(inst.url_prefix, expected)
+
+    def test_url_prefix_ascii_is_unaffected(self):
+        inst = self._makeOne(url_prefix="///api/v1///")
+        self.assertEqual(inst.url_prefix, "/api/v1")
+
     def test_goodvar_listen(self):
         inst = self._makeOne(listen="127.0.0.1")