diff --git a/utils/supportedCanonicalTimezones.ts b/utils/supportedCanonicalTimezones.ts
index 18c20ba..9ba1c6c 100644
--- a/utils/supportedCanonicalTimezones.ts
+++ b/utils/supportedCanonicalTimezones.ts
@@ -1,3 +1,22 @@
+/**
+ * Intl.supportedValuesOf is not shipped until Typescript 5.1
+ * Temporary workaround is from
+ * https://github.com/microsoft/TypeScript/issues/49231#issuecomment-1137251612
+ *
+ * TODO: When Typescript 5.1 is released with Deno (check with `deno --version`), remove this namespace extension.
+ */
+declare namespace Intl {
+  type Key =
+    | "calendar"
+    | "collation"
+    | "currency"
+    | "numberingSystem"
+    | "timeZone"
+    | "unit";
+
+  function supportedValuesOf(input: Key): string[];
+}
+
 /**
  * Get all canonical timezones that are supported by the browser or runtime,
  * or an empty array if the list is not available.