diff --git a/src/util/IntrusiveList.hxx b/src/util/IntrusiveList.hxx
index 2074220bc..84d874e47 100644
--- a/src/util/IntrusiveList.hxx
+++ b/src/util/IntrusiveList.hxx
@@ -207,6 +207,8 @@ class IntrusiveList {
 	}
 
 public:
+	using size_type = std::size_t;
+
 	constexpr IntrusiveList() noexcept = default;
 
 	IntrusiveList(IntrusiveList &&src) noexcept {
@@ -255,6 +257,10 @@ public:
 		return head.next == &head;
 	}
 
+	constexpr size_type size() const noexcept {
+		return std::distance(begin(), end());
+	}
+
 	void clear() noexcept {
 		if constexpr (std::is_base_of<SafeLinkIntrusiveListHook, T>::value) {
 			/* for SafeLinkIntrusiveListHook, we need to