diff --git a/libethcore/Exceptions.h b/libethcore/Exceptions.h
index c936b1f1b..8a15cd80f 100644
--- a/libethcore/Exceptions.h
+++ b/libethcore/Exceptions.h
@@ -25,7 +25,7 @@ class InvalidBlockHeaderFormat: public dev::Exception { public: InvalidBlockHead
 class InvalidUnclesHash: public dev::Exception {};
 class InvalidUncle: public dev::Exception {};
 class UncleTooOld: public dev::Exception {};
-class UncleInChain: public dev::Exception {};
+class UncleInChain: public dev::Exception { public: UncleInChain(h256Set _uncles, h256 _block): m_uncles(_uncles), m_block(_block) {} h256Set m_uncles; h256 m_block; virtual std::string description() const { return "Uncle in block already mentioned: Uncles " + toString(m_uncles) + " (" + m_block.abridged() + ")"; } };
 class DuplicateUncleNonce: public dev::Exception {};
 class InvalidStateRoot: public dev::Exception {};
 class InvalidTransactionsHash: public dev::Exception { public: InvalidTransactionsHash(h256 _head, h256 _real): m_head(_head), m_real(_real) {} h256 m_head; h256 m_real; virtual std::string description() const { return "Invalid transactions hash:  header says: " + toHex(m_head.ref()) + " block is:" + toHex(m_real.ref()); } };
diff --git a/libethereum/State.cpp b/libethereum/State.cpp
index a74b6ba18..8fa6141a5 100644
--- a/libethereum/State.cpp
+++ b/libethereum/State.cpp
@@ -577,6 +577,9 @@ u256 State::enact(bytesConstRef _block, BlockChain const* _bc, bool _checkNonce)
 	set<h256> knownUncles = _bc ? _bc->allUnclesFrom(m_currentBlock.parentHash) : set<h256>();
 	for (auto const& i: RLP(_block)[2])
 	{
+		if (knownUncles.count(sha3(i.data())))
+			throw UncleInChain(knownUncles, sha3(i.data()));
+
 		BlockInfo uncle = BlockInfo::fromHeader(i.data());
 		if (nonces.count(uncle.nonce))
 			throw DuplicateUncleNonce();
@@ -585,8 +588,6 @@ u256 State::enact(bytesConstRef _block, BlockChain const* _bc, bool _checkNonce)
 			BlockInfo uncleParent(_bc->block(uncle.parentHash));
 			if ((bigint)uncleParent.number < (bigint)m_currentBlock.number - 6)
 				throw UncleTooOld();
-			if (knownUncles.count(sha3(i.data())))
-				throw UncleInChain();
 			uncle.verifyParent(uncleParent);
 		}
 
@@ -725,7 +726,7 @@ void State::commitToMine(BlockChain const& _bc)
 			auto us = _bc.details(p).children;
 			assert(us.size() >= 1);	// must be at least 1 child of our grandparent - it's our own parent!
 			for (auto const& u: us)
-				if (!knownUncles.count(BlockInfo::headerHash(_bc.block(u))))	// ignore any uncles/mainline blocks that we know about. We use header-hash for this.
+				if (!knownUncles.count(u))	// ignore any uncles/mainline blocks that we know about.
 				{
 					BlockInfo ubi(_bc.block(u));
 					ubi.fillStream(unclesData, true);