diff --git a/src/sha1_ngcft1.cpp b/src/sha1_ngcft1.cpp
index aa364cd..94ee72a 100644
--- a/src/sha1_ngcft1.cpp
+++ b/src/sha1_ngcft1.cpp
@@ -335,21 +335,39 @@ void SHA1_NGCFT1::iterate(float delta) {
 
 			auto chunk_idx_opt = ce.get<Components::FT1ChunkSHA1Cache>().chunkIndex(chunk_hash);
 			if (chunk_idx_opt.has_value()) {
-				const auto& info = ce.get<Components::FT1InfoSHA1>();
 
-				uint8_t transfer_id {0};
-				if (_nft.NGC_FT1_send_init_private(
-					group_number, peer_number,
-					static_cast<uint32_t>(NGCFT1_file_kind::HASH_SHA1_CHUNK),
-					chunk_hash.data.data(), chunk_hash.size(),
-					chunkSize(info, chunk_idx_opt.value()),
-					&transfer_id
-				)) {
-					_sending_transfers
-						[combineIds(group_number, peer_number)]
-						[transfer_id] // TODO: also save index?
-							.v = SendingTransfer::Chunk{ce, chunk_idx_opt.value() * info.chunk_size};
+				// check if already sending
+				bool already_sending_to_this_peer = false;
+				if (_sending_transfers.count(combineIds(group_number, peer_number))) {
+					for (const auto& [_2, t] : _sending_transfers.at(combineIds(group_number, peer_number))) {
+						if (std::holds_alternative<SendingTransfer::Chunk>(t.v)) {
+							const auto& v = std::get<SendingTransfer::Chunk>(t.v);
+							if (v.content == ce && v.chunk_index == chunk_idx_opt.value()) {
+								// already sending
+								already_sending_to_this_peer = true;
+								break;
+							}
+						}
+					}
 				}
+
+				if (!already_sending_to_this_peer) {
+					const auto& info = ce.get<Components::FT1InfoSHA1>();
+
+					uint8_t transfer_id {0};
+					if (_nft.NGC_FT1_send_init_private(
+						group_number, peer_number,
+						static_cast<uint32_t>(NGCFT1_file_kind::HASH_SHA1_CHUNK),
+						chunk_hash.data.data(), chunk_hash.size(),
+						chunkSize(info, chunk_idx_opt.value()),
+						&transfer_id
+					)) {
+						_sending_transfers
+							[combineIds(group_number, peer_number)]
+							[transfer_id] // TODO: also save index?
+								.v = SendingTransfer::Chunk{ce, chunk_idx_opt.value()};
+					}
+				} // else just remove from queue
 			}
 			// remove from queue regardless
 			_queue_requested_chunk.pop_front();
@@ -640,14 +658,14 @@ bool SHA1_NGCFT1::onEvent(const Events::NGCFT1_recv_init& e) {
 		assert(idx_opt.has_value());
 
 		const auto& info = ce.get<Components::FT1InfoSHA1>();
-		uint64_t offset_into_file = uint64_t(info.chunk_size) * idx_opt.value();
 
 		// TODO: check e.file_size
+		assert(e.file_size == info.chunkSize(idx_opt.value()));
 
 		_receiving_transfers
 			[combineIds(e.group_number, e.peer_number)]
 			[e.transfer_id]
-				.v = ReceivingTransfer::Chunk{ce, offset_into_file};
+				.v = ReceivingTransfer::Chunk{ce, idx_opt.value()};
 
 		e.accept = true;
 
@@ -676,8 +694,8 @@ bool SHA1_NGCFT1::onEvent(const Events::NGCFT1_recv_data& e) {
 			info_data[i+e.data_offset] = e.data[i];
 		}
 	} else if (std::holds_alternative<ReceivingTransfer::Chunk>(tv)) {
-		const auto offset_into_file = std::get<ReceivingTransfer::Chunk>(tv).offset_into_file;
 		auto ce = std::get<ReceivingTransfer::Chunk>(tv).content;
+		const auto offset_into_file = std::get<ReceivingTransfer::Chunk>(tv).chunk_index * ce.get<Components::FT1InfoSHA1>().chunk_size;
 
 		assert(ce.all_of<Message::Components::Transfer::File>());
 		auto* file = ce.get<Message::Components::Transfer::File>().get();
@@ -717,8 +735,9 @@ bool SHA1_NGCFT1::onEvent(const Events::NGCFT1_send_data& e) {
 		}
 	} else if (std::holds_alternative<SendingTransfer::Chunk>(transfer.v)) {
 		auto& chunk_transfer = std::get<SendingTransfer::Chunk>(transfer.v);
+		const auto& info = chunk_transfer.content.get<Components::FT1InfoSHA1>();
 		// TODO: should we really use file?
-		const auto data = chunk_transfer.content.get<Message::Components::Transfer::File>()->read(chunk_transfer.offset_into_file + e.data_offset, e.data_size);
+		const auto data = chunk_transfer.content.get<Message::Components::Transfer::File>()->read((chunk_transfer.chunk_index * info.chunk_size) + e.data_offset, e.data_size);
 
 		// TODO: optimize
 		for (size_t i = 0; i < e.data_size && i < data.size(); i++) {
@@ -796,12 +815,12 @@ bool SHA1_NGCFT1::onEvent(const Events::NGCFT1_recv_done& e) {
 
 		updateMessages(ce);
 	} else if (std::holds_alternative<ReceivingTransfer::Chunk>(tv)) {
-		const auto offset_into_file = std::get<ReceivingTransfer::Chunk>(tv).offset_into_file;
 		auto ce = std::get<ReceivingTransfer::Chunk>(tv).content;
 		const auto& info = ce.get<Components::FT1InfoSHA1>();
 		auto& cc = ce.get<Components::FT1ChunkSHA1Cache>();
+		const auto chunk_index = std::get<ReceivingTransfer::Chunk>(tv).chunk_index;
+		const auto offset_into_file = chunk_index * info.chunk_size;
 
-		const auto chunk_index = offset_into_file/info.chunk_size;
 		assert(chunk_index < info.chunks.size());
 		const auto chunk_size = info.chunkSize(chunk_index);
 		assert(offset_into_file+chunk_size <= info.file_size);
diff --git a/src/sha1_ngcft1.hpp b/src/sha1_ngcft1.hpp
index bfd74c9..74eb555 100644
--- a/src/sha1_ngcft1.hpp
+++ b/src/sha1_ngcft1.hpp
@@ -53,7 +53,8 @@ class SHA1_NGCFT1 : public RegistryMessageModelEventI, public NGCFT1EventI {
 
 		struct Chunk {
 			ContentHandle content;
-			uint64_t offset_into_file;
+			size_t chunk_index; // <.< remove offset_into_file
+			//uint64_t offset_into_file;
 			// or data?
 			// if memmapped, this would be just a pointer
 		};
@@ -75,7 +76,8 @@ class SHA1_NGCFT1 : public RegistryMessageModelEventI, public NGCFT1EventI {
 
 		struct Chunk {
 			ContentHandle content;
-			uint64_t offset_into_file;
+			size_t chunk_index;
+			//uint64_t offset_into_file;
 			// or data?
 			// if memmapped, this would be just a pointer
 		};