diff --git a/libtransmission/serializer.h b/libtransmission/serializer.h
index 72f518461..89499afb7 100644
--- a/libtransmission/serializer.h
+++ b/libtransmission/serializer.h
@@ -383,6 +383,20 @@ bool set_if_changed(T& tgt, Fields const& fields, Key const key, Value val)
     return key_found && changed;
 }
 
+/**
+ * Check whether a key exists in a `fields` tuple.
+ */
+template<typename Fields, typename Key>
+[[nodiscard]] bool constexpr contains(Fields const& fields, Key const key)
+{
+    if constexpr (std::tuple_size_v<detail::remove_cvref_t<Fields>> == 0)
+    {
+        return false;
+    }
+
+    return std::apply([key](auto const&... field) { return ((field.key == key) || ...); }, fields);
+}
+
 /**
  * Get a field's value.
  *
diff --git a/tests/libtransmission/serializer-tests.cc b/tests/libtransmission/serializer-tests.cc
index 4c163bd90..2697d5f3b 100644
--- a/tests/libtransmission/serializer-tests.cc
+++ b/tests/libtransmission/serializer-tests.cc
@@ -297,6 +297,7 @@ TEST_F(SerializerTest, optionalRejectsWrongType)
 
 // ---
 
+using libtransmission::serializer::contains;
 using libtransmission::serializer::Field;
 using libtransmission::serializer::get_value;
 using libtransmission::serializer::load;
@@ -475,6 +476,24 @@ TEST_F(SerializerTest, setFloatScaled)
     EXPECT_DOUBLE_EQ(thing.d, val);
 }
 
+TEST_F(SerializerTest, containsMissingKey)
+{
+    EXPECT_FALSE(contains(Thing::Fields, TR_KEY_address));
+}
+
+TEST_F(SerializerTest, containsOk)
+{
+    EXPECT_TRUE(contains(Thing::Fields, TR_KEY_port));
+    EXPECT_TRUE(contains(Thing::Fields, TR_KEY_alt_speed_up));
+    EXPECT_TRUE(contains(Thing::Fields, TR_KEY_name));
+}
+
+TEST_F(SerializerTest, containsEmptyFields)
+{
+    static constexpr auto Empty = std::tuple{};
+    EXPECT_FALSE(contains(Empty, TR_KEY_name));
+}
+
 TEST_F(SerializerTest, getMissingKey)
 {
     auto thing = Thing{};