diff --git a/Userland/Libraries/LibWeb/WebIDL/Function.idl b/Userland/Libraries/LibWeb/WebIDL/Function.idl
new file mode 100644
index 0000000000..ef7d3a350e
--- /dev/null
+++ b/Userland/Libraries/LibWeb/WebIDL/Function.idl
@@ -0,0 +1,4 @@
+// https://webidl.spec.whatwg.org/#Function
+
+// FIXME: This should be a builtin type.
+callback Function = any (any... arguments);