diff --git a/include/duckhandy/bitfield_pack.hpp b/include/duckhandy/bitfield_pack.hpp
index 93a2bfc..a6fb188 100644
--- a/include/duckhandy/bitfield_pack.hpp
+++ b/include/duckhandy/bitfield_pack.hpp
@@ -55,29 +55,47 @@ namespace dhandy {
 		struct SizeAndOffs {
 			std::size_t size, offset;
 		};
+		struct IndexAndSize {
+			std::size_t index, size;
+		};
 
 		template <std::size_t Sum>
-		[[gnu::pure]]
 		constexpr inline SizeAndOffs size_and_offset_impl (std::size_t) {
 			throw std::out_of_range("Requested pack index out of range");
 		}
-
 		template <std::size_t Sum, std::size_t Sz, std::size_t... Sizes>
-		[[gnu::pure]]
 		constexpr inline SizeAndOffs size_and_offset_impl (std::size_t index) {
 			return (index ? size_and_offset_impl<Sum + Sz, Sizes...>(index - 1) : SizeAndOffs{Sz, Sum});
 		}
-
 		template <std::size_t... Sizes>
-		[[gnu::pure]]
 		constexpr inline SizeAndOffs size_and_offset (std::size_t index) {
 			return size_and_offset_impl<0, Sizes...>(index);
 		}
 
+		template <std::size_t CurrMax, std::size_t MaxIdx, std::size_t Idx>
+		constexpr inline IndexAndSize index_and_size_impl() {
+			throw std::runtime_error("Should not be reached");
+		}
+		template <std::size_t CurrMax, std::size_t MaxIdx, std::size_t Idx, std::size_t Sz, std::size_t... Sizes>
+		constexpr inline IndexAndSize index_and_size_impl() {
+			return (Idx ? index_and_size_impl<
+				(CurrMax > Sz ? CurrMax : Sz),
+				(CurrMax > Sz ? MaxIdx : Idx),
+				Idx - 1,
+				Sizes...
+			>() : IndexAndSize{(CurrMax > Sz ? MaxIdx : Idx) - 1, CurrMax > Sz ? CurrMax : Sz});
+		}
+		template <std::size_t Sz, std::size_t... Sizes>
+		constexpr inline IndexAndSize index_and_size() {
+			return index_and_size_impl<Sz, sizeof...(Sizes), sizeof...(Sizes), Sz, Sizes...>();
+		}
+
 		template <typename T, std::size_t... Sizes>
 		struct BitfieldFacts {
 			static const constexpr std::size_t Sum = size_and_offset<Sizes...>(sizeof...(Sizes) - 1).size + size_and_offset<Sizes...>(sizeof...(Sizes) - 1).offset;
 			static const constexpr std::size_t ElementCount = (Sum + CHAR_BIT * sizeof(T) - 1) / (CHAR_BIT *sizeof(T));
+			static const constexpr std::size_t LargestIndex = index_and_size<Sizes...>().index;
+			static const constexpr std::size_t LargestSize = index_and_size<Sizes...>().size;
 		};
 
 		template <typename T>
@@ -96,9 +114,11 @@ namespace dhandy {
 
 	template <typename T, std::size_t... Sizes>
 	class BitfieldPack : private implem::BitfieldData<T, implem::BitfieldFacts<T, Sizes...>::ElementCount> {
+		typedef implem::BitfieldFacts<T, Sizes...> Facts;
 		template <std::size_t Idx, typename U, std::size_t... S> friend U get (const BitfieldPack<U, S...>&);
 		template <std::size_t Idx, typename U, typename V, std::size_t... S> friend void set (BitfieldPack<U, S...>&, V);
-		typedef implem::BitfieldData<T, implem::BitfieldFacts<T, Sizes...>::ElementCount> base_type;
+		typedef implem::BitfieldData<T, Facts::ElementCount> base_type;
+		static_assert(Facts::LargestSize <= sizeof(T) * CHAR_BIT, "Bitfield size can't be larget than the data type itself");
 	public:
 		BitfieldPack (T init=T{}) : base_type(init) {}
 	};
@@ -109,6 +129,7 @@ namespace dhandy {
 		using implem::BitfieldData;
 		using implem::make_mask;
 
+		static_assert(Idx < sizeof...(Sizes), "Index out of bounds");
 		const constexpr auto so = size_and_offset<Sizes...>(Idx);
 		const constexpr std::size_t index = so.offset / (sizeof(T) * CHAR_BIT);
 		const constexpr std::size_t reloffs = so.offset % (sizeof(T) * CHAR_BIT);
@@ -131,6 +152,7 @@ namespace dhandy {
 		using implem::BitfieldData;
 		using implem::make_mask;
 
+		static_assert(Idx < sizeof...(Sizes), "Index out of bounds");
 		const constexpr auto so = size_and_offset<Sizes...>(Idx);
 		const constexpr std::size_t index = so.offset / (sizeof(T) * CHAR_BIT);
 		const constexpr std::size_t reloffs = so.offset % (sizeof(T) * CHAR_BIT);
@@ -138,7 +160,7 @@ namespace dhandy {
 
 		T& bottom = static_cast<BitfieldData<T, index + 1>&>(pack).value();
 		bottom &= ~(make_mask<T>(so.size) << reloffs);
-		bottom |= static_cast<T>((val << reloffs) & make_mask<T>(so.size));
+		bottom |= static_cast<T>((val & make_mask<T>(so.size)) << reloffs);
 
 		if (bleeds_into_next) {
 			const std::size_t safe_index = index + 2 - not bleeds_into_next;
diff --git a/test/unit/bitfield_pack_test.cpp b/test/unit/bitfield_pack_test.cpp
index cad75bb..0ab818d 100644
--- a/test/unit/bitfield_pack_test.cpp
+++ b/test/unit/bitfield_pack_test.cpp
@@ -20,16 +20,61 @@
 #include <cstdint>
 
 TEST_CASE ("Check correctness in BitfieldPack", "[BitfieldPack][containers]") {
-	dhandy::BitfieldPack<uint8_t, 4, 7, 1> pack(0xAA);
-	CHECK(sizeof(pack) == sizeof(uint8_t) * 2);
-
-	CHECK(dhandy::get<0>(pack) == 0b1010U);
-	CHECK(dhandy::get<1>(pack) == 0b0101010U);
-	CHECK(dhandy::get<2>(pack) == 0b1U);
-
-	dhandy::set<0>(pack, 2);
-	CHECK(dhandy::get<0>(pack) == 2);
-	dhandy::set<1>(pack, 50);
-	CHECK(dhandy::get<1>(pack) == 50);
-	CHECK(dhandy::get<2>(pack) == 0b1U);
+	using dhandy::set;
+	using dhandy::get;
+
+	{
+		dhandy::BitfieldPack<uint8_t, 4, 7, 1> pack(0xAA);
+		CHECK(sizeof(pack) == sizeof(uint8_t) * 2);
+
+		CHECK(get<0>(pack) == 0b1010U);
+		CHECK(get<1>(pack) == 0b0101010U);
+		CHECK(get<2>(pack) == 0b1U);
+
+		set<0>(pack, 2);
+		CHECK(get<0>(pack) == 2);
+		set<1>(pack, 50);
+		CHECK(get<1>(pack) == 50);
+		CHECK(get<2>(pack) == 0b1U);
+		CHECK(get<0>(pack) == 2);
+	}
+
+	{
+		dhandy::BitfieldPack<uint16_t, 16, 5, 8, 11, 3, 1, 1> pack;
+		set<6>(pack, 1);
+		CHECK(get<0>(pack) == 0);
+		CHECK(get<1>(pack) == 0);
+		CHECK(get<2>(pack) == 0);
+		CHECK(get<3>(pack) == 0);
+		CHECK(get<4>(pack) == 0);
+		CHECK(get<5>(pack) == 0);
+		CHECK(get<6>(pack) == 1);
+
+		set<6>(pack, 0);
+		CHECK(get<6>(pack) == 0);
+
+		set<6>(pack, 1);
+		set<1>(pack, 5);
+		CHECK(get<0>(pack) == 0);
+		CHECK(get<1>(pack) == 5);
+		CHECK(get<2>(pack) == 0);
+		CHECK(get<3>(pack) == 0);
+		CHECK(get<4>(pack) == 0);
+		CHECK(get<5>(pack) == 0);
+		CHECK(get<6>(pack) == 1);
+
+		set<1>(pack, 0);
+		CHECK(get<1>(pack) == 0);
+
+		set<6>(pack, 1);
+		set<1>(pack, 5);
+		set<3>(pack, 0b10011001101);
+		CHECK(get<0>(pack) == 0);
+		CHECK(get<1>(pack) == 5);
+		CHECK(get<2>(pack) == 0);
+		CHECK(get<3>(pack) == 0b10011001101);
+		CHECK(get<4>(pack) == 0);
+		CHECK(get<5>(pack) == 0);
+		CHECK(get<6>(pack) == 1);
+	}
 }