diff --git a/types/index.d.ts b/types/index.d.ts
index 1a77877..018527e 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -34,6 +34,7 @@ declare namespace express_prom_bundle {
     normalizePath?: NormalizePathEntry[] | NormalizePathFn;
     formatStatusCode?: NormalizeStatusCodeFn;
     transformLabels?: TransformLabelsFn;
+    httpDurationMetricName?: string;
 
     // https://github.com/disjunction/url-value-parser#options
     urlValueParser?: {