diff --git a/package-lock.json b/package-lock.json
index 788e00d..dafd6c4 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -11129,7 +11129,7 @@
     },
     "packages/events": {
       "name": "@nhsdigital/nhs-notify-event-schemas-letter-rendering",
-      "version": "1.1.1",
+      "version": "1.1.2",
       "dependencies": {
         "@asyncapi/bundler": "^0.6.4",
         "zod": "^4.1.11"
diff --git a/packages/events/package.json b/packages/events/package.json
index 39d55d3..0f74898 100644
--- a/packages/events/package.json
+++ b/packages/events/package.json
@@ -40,5 +40,5 @@
     "test:unit": "jest",
     "prepare": "npm run build"
   },
-  "version": "1.1.1"
+  "version": "1.1.2"
 }
diff --git a/packages/events/src/events/event-envelope.ts b/packages/events/src/events/event-envelope.ts
index e2f2181..5e1f61d 100644
--- a/packages/events/src/events/event-envelope.ts
+++ b/packages/events/src/events/event-envelope.ts
@@ -10,7 +10,7 @@ export function EventEnvelope<TData extends z.ZodTypeAny>(
 ) {
   const statusRegex = statuses.map((s) => s.toLowerCase()).join("|");
   const subjectPrefixRegex = subjectPrefix
-    ? `${subjectPrefix}/[a-z0-9-]+/`
+    ? `${subjectPrefix}/[a-zA-Z0-9_-]+/`
     : "";
   const subjectExamplePrefix = subjectPrefix ? `${subjectPrefix}/abc-123/` : "";