diff --git a/libethereum/BlockChain.cpp b/libethereum/BlockChain.cpp
index 9921342d7..8fda03a88 100644
--- a/libethereum/BlockChain.cpp
+++ b/libethereum/BlockChain.cpp
@@ -1272,7 +1272,7 @@ bytes BlockChain::headerData(h256 const& _hash) const
 	return BlockInfo::extractHeader(&m_blocks[_hash]).data().toBytes();
 }
 
-Block BlockChain::genesisBlock(OverlayDB const& _db)
+Block BlockChain::genesisBlock(OverlayDB const& _db) const
 {
 	Block ret(_db, BaseState::Empty);
 	dev::eth::commit(m_genesisState, ret.mutableState().m_state);		// bit horrible. maybe consider a better way of constructing it?
diff --git a/libethereum/BlockChain.h b/libethereum/BlockChain.h
index f8094fe23..581c0eee8 100644
--- a/libethereum/BlockChain.h
+++ b/libethereum/BlockChain.h
@@ -286,7 +286,7 @@ public:
 	template <class T> void setOnBad(T const& _t) { m_onBad = _t; }
 
 	/// Get a pre-made genesis State object.
-	Block genesisBlock(OverlayDB const& _db);
+	Block genesisBlock(OverlayDB const& _db) const;
 
 	/// Verify block and prepare it for enactment
 	virtual VerifiedBlockRef verifyBlock(bytesConstRef _block, std::function<void(Exception&)> const& _onBad, ImportRequirements::value _ir = ImportRequirements::OutOfOrderChecks) const = 0;