diff --git a/Userland/Libraries/LibWeb/HighResolutionTime/CoarsenTime.cpp b/Userland/Libraries/LibWeb/HighResolutionTime/CoarsenTime.cpp
index 0d5739e629..17dcaa47dd 100644
--- a/Userland/Libraries/LibWeb/HighResolutionTime/CoarsenTime.cpp
+++ b/Userland/Libraries/LibWeb/HighResolutionTime/CoarsenTime.cpp
@@ -9,7 +9,7 @@
 namespace Web::HighResolutionTime {
 
 // https://w3c.github.io/hr-time/#dfn-coarsen-time
-double coarsen_time(double timestamp, bool cross_origin_isolated_capability)
+DOMHighResTimeStamp coarsen_time(DOMHighResTimeStamp timestamp, bool cross_origin_isolated_capability)
 {
     // FIXME: Implement this.
     (void)cross_origin_isolated_capability;
diff --git a/Userland/Libraries/LibWeb/HighResolutionTime/CoarsenTime.h b/Userland/Libraries/LibWeb/HighResolutionTime/CoarsenTime.h
index 91fa541c46..4752eaae08 100644
--- a/Userland/Libraries/LibWeb/HighResolutionTime/CoarsenTime.h
+++ b/Userland/Libraries/LibWeb/HighResolutionTime/CoarsenTime.h
@@ -6,9 +6,10 @@
 
 #pragma once
 
+#include <LibWeb/HighResolutionTime/DOMHighResTimeStamp.h>
+
 namespace Web::HighResolutionTime {
 
-// https://w3c.github.io/hr-time/#dfn-coarsen-time
-double coarsen_time(double timestamp, bool cross_origin_isolated_capability = false);
+DOMHighResTimeStamp coarsen_time(DOMHighResTimeStamp timestamp, bool cross_origin_isolated_capability = false);
 
 }
diff --git a/Userland/Libraries/LibWeb/HighResolutionTime/DOMHighResTimeStamp.h b/Userland/Libraries/LibWeb/HighResolutionTime/DOMHighResTimeStamp.h
new file mode 100644
index 0000000000..277ad93a3c
--- /dev/null
+++ b/Userland/Libraries/LibWeb/HighResolutionTime/DOMHighResTimeStamp.h
@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+namespace Web::HighResolutionTime {
+
+// https://w3c.github.io/hr-time/#dom-domhighrestimestamp
+using DOMHighResTimeStamp = double;
+
+}