diff --git a/keystoneauth1/discover.py b/keystoneauth1/discover.py
index 00b9752a..f03ffbfd 100644
--- a/keystoneauth1/discover.py
+++ b/keystoneauth1/discover.py
@@ -1415,6 +1415,18 @@ def get_discovery(session, url, cache=None, authenticated=False):
     if session.auth and hasattr(session.auth, '_discovery_cache'):
         caches.append(session.auth._discovery_cache)
 
+    # https://example.com and https://example.com/ should be treated the same
+    # for caching purposes.
+    parsed_url = urllib.parse.urlparse(url)
+    if parsed_url.path in ('', '/'):
+        url = urllib.parse.ParseResult(
+            parsed_url.scheme,
+            parsed_url.netloc,
+            '',
+            parsed_url.params,
+            parsed_url.query,
+            parsed_url.fragment).geturl()
+
     for cache in caches:
         disc = cache.get(url)
 
diff --git a/keystoneauth1/tests/unit/identity/test_identity_common.py b/keystoneauth1/tests/unit/identity/test_identity_common.py
index 46fe0aee..2d4c1e9c 100644
--- a/keystoneauth1/tests/unit/identity/test_identity_common.py
+++ b/keystoneauth1/tests/unit/identity/test_identity_common.py
@@ -341,6 +341,31 @@ class CommonIdentityTests(object):
 
         self.assertIn(self.TEST_COMPUTE_ADMIN, discovery_cache.keys())
 
+    def test_discovery_trailing_slash(self):
+        # The discovery cache should treat root urls the same whether they have
+        # a slash or not. If the url is called a second time (meaning the cache
+        # didn't work, we'll hit the 500 error.
+        self.requests_mock.get(
+            'https://example.com', [
+                {'json': self.TEST_DISCOVERY},
+                {'status_code': 500}
+            ])
+
+        sess = session.Session()
+        discovery_cache = {}
+
+        expected_url = 'https://example.com/v2.0'
+
+        for test_endpoint in ('https://example.com', 'https://example.com/'):
+            disc = discover.get_discovery(
+                sess, test_endpoint, cache=discovery_cache)
+            url = disc.url_for(('2', '0'))
+
+            self.assertEqual(expected_url, url)
+
+        self.assertIn('https://example.com', discovery_cache.keys())
+        self.assertNotIn('https://example.com/', discovery_cache.keys())
+
     def test_discovering_with_no_data(self):
         # which returns discovery information pointing to TEST_URL but there is
         # no data there.
diff --git a/releasenotes/notes/cache-trailing-slash-3663c86cd9754379.yaml b/releasenotes/notes/cache-trailing-slash-3663c86cd9754379.yaml
new file mode 100644
index 00000000..a93167ee
--- /dev/null
+++ b/releasenotes/notes/cache-trailing-slash-3663c86cd9754379.yaml
@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    Fixed an issue where https://example.com and https://example.com/ were
+    being treated as different urls in the discovery cache resulting in a
+    second unneeded discovery call when someone sets an ``endpoint_override``
+    that didn't match the trailing-slash form given by that service's
+    discovery document.