diff --git a/signal-server-openapi.yaml b/signal-server-openapi.yaml
index ebfc3c3a6..36a617188 100644
--- a/signal-server-openapi.yaml
+++ b/signal-server-openapi.yaml
@@ -1216,6 +1216,10 @@ paths:
       - Certificate
       operationId: getGroupAuthenticationCredentials
       parameters:
+      - name: User-Agent
+        in: header
+        schema:
+          type: string
       - name: redemptionStartSeconds
         in: query
         schema: