diff --git a/src/RemoteTagCache.hxx b/src/RemoteTagCache.hxx
index fdaff2770..523321350 100644
--- a/src/RemoteTagCache.hxx
+++ b/src/RemoteTagCache.hxx
@@ -85,9 +85,9 @@ class RemoteTagCache final {
 
 	IntrusiveHashSet<
 		Item, 127,
-		IntrusiveHashSetOperators<std::hash<std::string_view>,
-					  std::equal_to<std::string_view>,
-					  Item::GetUri>,
+		IntrusiveHashSetOperators<Item, Item::GetUri,
+					  std::hash<std::string_view>,
+					  std::equal_to<std::string_view>>,
 		IntrusiveHashSetBaseHookTraits<Item>,
 		IntrusiveHashSetOptions{.constant_time_size = true}> map;
 
diff --git a/src/input/cache/Manager.hxx b/src/input/cache/Manager.hxx
index bf160bb12..40b0e970f 100644
--- a/src/input/cache/Manager.hxx
+++ b/src/input/cache/Manager.hxx
@@ -32,9 +32,9 @@ class InputCacheManager {
 	IntrusiveList<InputCacheItem> items_by_time;
 
 	IntrusiveHashSet<InputCacheItem, 127,
-			 IntrusiveHashSetOperators<std::hash<std::string_view>,
-						   std::equal_to<std::string_view>,
-						   ItemGetUri>> items_by_uri;
+			 IntrusiveHashSetOperators<InputCacheItem, ItemGetUri,
+						   std::hash<std::string_view>,
+						   std::equal_to<std::string_view>>> items_by_uri;
 
 public:
 	explicit InputCacheManager(const InputCacheConfig &config) noexcept;
diff --git a/src/tag/Pool.cxx b/src/tag/Pool.cxx
index d48744c97..9d78b5641 100644
--- a/src/tag/Pool.cxx
+++ b/src/tag/Pool.cxx
@@ -78,9 +78,9 @@ TagPoolItem::Create(TagType type,
 }
 
 static IntrusiveHashSet<TagPoolItem, 16384,
-	IntrusiveHashSetOperators<TagPoolKey::Hash,
-				  std::equal_to<TagPoolKey>,
-				  TagPoolItem::GetKey>,
+	IntrusiveHashSetOperators<TagPoolItem, TagPoolItem::GetKey,
+				  TagPoolKey::Hash,
+				  std::equal_to<TagPoolKey>>,
 	IntrusiveHashSetMemberHookTraits<&TagPoolItem::hash_set_hook>,
 	IntrusiveHashSetOptions{.zero_initialized = true}> tag_pool;
 
diff --git a/src/util/IntrusiveHashSet.hxx b/src/util/IntrusiveHashSet.hxx
index 9a578566f..25e929961 100644
--- a/src/util/IntrusiveHashSet.hxx
+++ b/src/util/IntrusiveHashSet.hxx
@@ -8,6 +8,7 @@
 
 #include <algorithm> // for std::all_of()
 #include <array>
+#include <concepts> // for std::regular_invocable
 #include <numeric> // for std::accumulate()
 
 struct IntrusiveHashSetOptions {
@@ -94,8 +95,11 @@ struct IntrusiveHashSetMemberHookTraits {
  * @param GetKey a function object which extracts the "key" part of an
  * item
  */
-template<typename Hash, typename Equal,
-	 typename GetKey=std::identity>
+template<typename T,
+	 std::regular_invocable<const T &> GetKey,
+	 std::regular_invocable<std::invoke_result_t<GetKey, const T &>> Hash,
+	 std::predicate<std::invoke_result_t<GetKey, const T &>,
+			std::invoke_result_t<GetKey, const T &>> Equal>
 struct IntrusiveHashSetOperators {
 	using hasher = Hash;
 	using key_equal = Equal;
diff --git a/test/util/TestIntrusiveHashSet.cxx b/test/util/TestIntrusiveHashSet.cxx
index 42d5c1839..f87da73f8 100644
--- a/test/util/TestIntrusiveHashSet.cxx
+++ b/test/util/TestIntrusiveHashSet.cxx
@@ -39,7 +39,8 @@ TEST(IntrusiveHashSet, Basic)
 	IntItem a{1}, b{2}, c{3}, d{4}, e{5}, f{1};
 
 	IntrusiveHashSet<IntItem, 3,
-			 IntrusiveHashSetOperators<IntItem::Hash,
+			 IntrusiveHashSetOperators<IntItem, std::identity,
+						   IntItem::Hash,
 						   IntItem::Equal>> set;
 
 	{
@@ -124,7 +125,8 @@ TEST(IntrusiveHashSet, Multi)
 	IntItem a{1}, b{2}, c{3}, d{4}, e{5}, f{1};
 
 	IntrusiveHashSet<IntItem, 3,
-			 IntrusiveHashSetOperators<IntItem::Hash,
+			 IntrusiveHashSetOperators<IntItem, std::identity,
+						   IntItem::Hash,
 						   IntItem::Equal>> set;
 
 	set.insert(a);
@@ -179,15 +181,15 @@ TEST(IntrusiveHashSet, Tag)
 	TaggedItem one{1, 11}, two{2, 22};
 
 	IntrusiveHashSet<TaggedItem, 3,
-			 IntrusiveHashSetOperators<std::hash<int>,
-						   std::equal_to<int>,
-						   GetA>,
+			 IntrusiveHashSetOperators<TaggedItem, GetA,
+						   std::hash<int>,
+						   std::equal_to<int>>,
 			 IntrusiveHashSetBaseHookTraits<TaggedItem, A>> a;
 
 	IntrusiveHashSet<TaggedItem, 3,
-			 IntrusiveHashSetOperators<std::hash<int>,
-						   std::equal_to<int>,
-						   GetB>,
+			 IntrusiveHashSetOperators<TaggedItem, GetB,
+						   std::hash<int>,
+						   std::equal_to<int>>,
 			 IntrusiveHashSetBaseHookTraits<TaggedItem, B>> b;
 
 	EXPECT_TRUE(a.empty());