diff --git a/hc/api/decorators.py b/hc/api/decorators.py
index 7b87863b..366a2636 100644
--- a/hc/api/decorators.py
+++ b/hc/api/decorators.py
@@ -1,4 +1,5 @@
 import json
+import re
 import uuid
 from functools import wraps
 
@@ -7,13 +8,13 @@ from django.http import (HttpResponseBadRequest, HttpResponseForbidden,
                          JsonResponse)
 from hc.lib.jsonschema import ValidationError, validate
 
+RE_UUID = re.compile("^[a-fA-F0-9]{8}-[a-fA-F0-9]{4}-4[a-fA-F0-9]{3}-[8|9|aA|bB][a-fA-F0-9]{3}-[a-fA-F0-9]{12}$")
+
 
 def uuid_or_400(f):
     @wraps(f)
     def wrapper(request, *args, **kwds):
-        try:
-            uuid.UUID(args[0])
-        except ValueError:
+        if not RE_UUID.match(args[0]):
             return HttpResponseBadRequest()
 
         return f(request, *args, **kwds)
diff --git a/hc/api/tests/test_ping.py b/hc/api/tests/test_ping.py
index fc5b1724..94080061 100644
--- a/hc/api/tests/test_ping.py
+++ b/hc/api/tests/test_ping.py
@@ -11,30 +11,30 @@ class PingTestCase(TestCase):
 
     def test_it_works(self):
         r = self.client.get("/ping/%s/" % self.check.code)
-        assert r.status_code == 200
+        self.assertEqual(r.status_code, 200)
 
         self.check.refresh_from_db()
         self.assertEqual(self.check.status, "up")
         self.assertEqual(self.check.alert_after, self.check.get_alert_after())
 
         ping = Ping.objects.latest("id")
-        assert ping.scheme == "http"
+        self.assertEqual(ping.scheme, "http")
 
     def test_it_changes_status_of_paused_check(self):
         self.check.status = "paused"
         self.check.save()
 
         r = self.client.get("/ping/%s/" % self.check.code)
-        assert r.status_code == 200
+        self.assertEqual(r.status_code, 200)
 
         self.check.refresh_from_db()
-        assert self.check.status == "up"
+        self.assertEqual(self.check.status, "up")
 
     def test_post_works(self):
         csrf_client = Client(enforce_csrf_checks=True)
         r = csrf_client.post("/ping/%s/" % self.check.code, "hello world",
                              content_type="text/plain")
-        assert r.status_code == 200
+        self.assertEqual(r.status_code, 200)
 
         self.check.refresh_from_db()
         self.assertEqual(self.check.last_ping_body, "hello world")
@@ -45,16 +45,21 @@ class PingTestCase(TestCase):
     def test_head_works(self):
         csrf_client = Client(enforce_csrf_checks=True)
         r = csrf_client.head("/ping/%s/" % self.check.code)
-        assert r.status_code == 200
-        assert Ping.objects.count() == 1
+        self.assertEqual(r.status_code, 200)
+        self.assertEqual(Ping.objects.count(), 1)
 
     def test_it_handles_bad_uuid(self):
         r = self.client.get("/ping/not-uuid/")
-        assert r.status_code == 400
+        self.assertEqual(r.status_code, 400)
+
+    def test_it_rejects_alternative_uuid_formats(self):
+        # This uuid is missing separators. uuid.UUID() would accept it.
+        r = self.client.get("/ping/07c2f54898504b27af5d6c9dc157ec02/")
+        self.assertEqual(r.status_code, 400)
 
     def test_it_handles_missing_check(self):
         r = self.client.get("/ping/07c2f548-9850-4b27-af5d-6c9dc157ec02/")
-        assert r.status_code == 404
+        self.assertEqual(r.status_code, 404)
 
     def test_it_handles_120_char_ua(self):
         ua = ("Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_4) "
@@ -62,19 +67,19 @@ class PingTestCase(TestCase):
               "Chrome/44.0.2403.89 Safari/537.36")
 
         r = self.client.get("/ping/%s/" % self.check.code, HTTP_USER_AGENT=ua)
-        assert r.status_code == 200
+        self.assertEqual(r.status_code, 200)
 
         ping = Ping.objects.latest("id")
-        assert ping.ua == ua
+        self.assertEqual(ping.ua, ua)
 
     def test_it_truncates_long_ua(self):
         ua = "01234567890" * 30
 
         r = self.client.get("/ping/%s/" % self.check.code, HTTP_USER_AGENT=ua)
-        assert r.status_code == 200
+        self.assertEqual(r.status_code, 200)
 
         ping = Ping.objects.latest("id")
-        assert len(ping.ua) == 200
+        self.assertEqual(len(ping.ua), 200)
         assert ua.startswith(ping.ua)
 
     def test_it_reads_forwarded_ip(self):
@@ -82,22 +87,22 @@ class PingTestCase(TestCase):
         r = self.client.get("/ping/%s/" % self.check.code,
                             HTTP_X_FORWARDED_FOR=ip)
         ping = Ping.objects.latest("id")
-        assert r.status_code == 200
-        assert ping.remote_addr == "1.1.1.1"
+        self.assertEqual(r.status_code, 200)
+        self.assertEqual(ping.remote_addr, "1.1.1.1")
 
         ip = "1.1.1.1, 2.2.2.2"
         r = self.client.get("/ping/%s/" % self.check.code,
                             HTTP_X_FORWARDED_FOR=ip, REMOTE_ADDR="3.3.3.3")
         ping = Ping.objects.latest("id")
-        assert r.status_code == 200
-        assert ping.remote_addr == "1.1.1.1"
+        self.assertEqual(r.status_code, 200)
+        self.assertEqual(ping.remote_addr, "1.1.1.1")
 
     def test_it_reads_forwarded_protocol(self):
         r = self.client.get("/ping/%s/" % self.check.code,
                             HTTP_X_FORWARDED_PROTO="https")
         ping = Ping.objects.latest("id")
-        assert r.status_code == 200
-        assert ping.scheme == "https"
+        self.assertEqual(r.status_code, 200)
+        self.assertEqual(ping.scheme, "https")
 
     def test_it_never_caches(self):
         r = self.client.get("/ping/%s/" % self.check.code)