diff --git a/hc/api/schemas.py b/hc/api/schemas.py
index 5f6acf05..75f05e96 100644
--- a/hc/api/schemas.py
+++ b/hc/api/schemas.py
@@ -4,7 +4,7 @@ check = {
     "type": "object",
     "properties": {
         "name": {"type": "string", "maxLength": 100},
-        "slug": {"type": "string", "pattern": "^[a-zA-Z0-9-_]*$"},
+        "slug": {"type": "string", "pattern": "^[a-z0-9-_]*$"},
         "desc": {"type": "string"},
         "tags": {"type": "string", "maxLength": 500},
         "timeout": {"type": "number", "minimum": 60, "maximum": 31536000},
diff --git a/hc/api/tests/test_create_check.py b/hc/api/tests/test_create_check.py
index e1e5066f..93bbe817 100644
--- a/hc/api/tests/test_create_check.py
+++ b/hc/api/tests/test_create_check.py
@@ -387,8 +387,9 @@ class CreateCheckTestCase(BaseTestCase):
         self.assertEqual(check.slug, "")
 
     def test_it_handles_invalid_slug(self):
-        r = self.post({"name": "Foo", "slug": "Hey!"}, v=3)
-        self.assertEqual(r.status_code, 400)
-        self.assertEqual(
-            r.json()["error"], "json validation error: slug does not match pattern"
-        )
+        for slug in ["Uppercase", "special!", "look spaces"]:
+            r = self.post({"name": "Foo", "slug": "Hey!"}, v=3)
+            self.assertEqual(r.status_code, 400)
+            self.assertEqual(
+                r.json()["error"], "json validation error: slug does not match pattern"
+            )
diff --git a/static/js/slug-suggestions.js b/static/js/slug-suggestions.js
index d874dd7f..cc41d5de 100644
--- a/static/js/slug-suggestions.js
+++ b/static/js/slug-suggestions.js
@@ -23,7 +23,7 @@ $(function () {
             if (suggested) {
                 help.html(`Suggested value: <code>${suggested}</code>`);
             } else {
-                help.text("Allowed characters: a-z, A-Z, 0-9, hyphens, underscores.");
+                help.text("Allowed characters: a-z, 0-9, hyphens, underscores.");
             }
 
             btn.attr("disabled", !suggested);
diff --git a/templates/front/add_check_modal.html b/templates/front/add_check_modal.html
index 56e03238..e154fb20 100644
--- a/templates/front/add_check_modal.html
+++ b/templates/front/add_check_modal.html
@@ -40,7 +40,7 @@
                                     type="text"
                                     maxlength="100"
                                     value="{{ check.slug }}"
-                                    pattern="[a-zA-Z0-9_-]+"
+                                    pattern="[a-z0-9_-]+"
                                     class="form-control" />
                                 <span class="input-group-btn">
                                     <button
diff --git a/templates/front/update_name_modal.html b/templates/front/update_name_modal.html
index dc4ebe37..1a123bbc 100644
--- a/templates/front/update_name_modal.html
+++ b/templates/front/update_name_modal.html
@@ -45,7 +45,7 @@
                                     type="text"
                                     maxlength="100"
                                     value="{{ check.slug }}"
-                                    pattern="[a-zA-Z0-9_-]+"
+                                    pattern="[a-z0-9_-]+"
                                     data-src-id="update-name-input"
                                     data-btn-id="use-suggested"
                                     data-preview-id="slug-help"