diff --git a/substrate/core/client/db/Cargo.toml b/substrate/core/client/db/Cargo.toml
index cc6e38d017..2944ab533b 100644
--- a/substrate/core/client/db/Cargo.toml
+++ b/substrate/core/client/db/Cargo.toml
@@ -21,12 +21,12 @@ parity-codec = { version = "3.2", features = ["derive"] }
 executor = { package = "substrate-executor", path = "../../executor" }
 state_db = { package = "substrate-state-db", path = "../../state-db" }
 trie = { package = "substrate-trie", path = "../../trie" }
+consensus_common = { package = "substrate-consensus-common", path = "../../consensus/common" }
 
 [dev-dependencies]
 kvdb-memorydb = { git = "https://github.com/paritytech/parity-common", rev="b0317f649ab2c665b7987b8475878fc4d2e1f81d" }
 substrate-keyring = { path = "../../keyring" }
 test-client = { package = "substrate-test-client", path = "../../test-client" }
-consensus_common = { package = "substrate-consensus-common", path = "../../consensus/common" }
 env_logger = { version = "0.6" }
 
 [features]
diff --git a/substrate/core/client/db/src/cache/mod.rs b/substrate/core/client/db/src/cache/mod.rs
index 93555f3c15..b5dd45f11d 100644
--- a/substrate/core/client/db/src/cache/mod.rs
+++ b/substrate/core/client/db/src/cache/mod.rs
@@ -26,6 +26,7 @@ use client::error::Result as ClientResult;
 use parity_codec::{Encode, Decode};
 use runtime_primitives::generic::BlockId;
 use runtime_primitives::traits::{Block as BlockT, Header as HeaderT, NumberFor, As};
+use consensus_common::well_known_cache_keys::Id as CacheKeyId;
 use crate::utils::{self, COLUMN_META};
 
 use self::list_cache::ListCache;
@@ -64,7 +65,7 @@ impl<T> CacheItemT for T where T: Clone + Decode + Encode + PartialEq {}
 
 /// Database-backed blockchain data cache.
 pub struct DbCache<Block: BlockT> {
-	cache_at: HashMap<Vec<u8>, ListCache<Block, Vec<u8>, self::list_storage::DbStorage>>,
+	cache_at: HashMap<CacheKeyId, ListCache<Block, Vec<u8>, self::list_storage::DbStorage>>,
 	db: Arc<KeyValueDB>,
 	key_lookup_column: Option<u32>,
 	header_column: Option<u32>,
@@ -112,7 +113,7 @@ impl<Block: BlockT> DbCache<Block> {
 	}
 
 	/// Creates `ListCache` with the given name or returns a reference to the existing.
-	fn get_cache(&mut self, name: Vec<u8>) -> &mut ListCache<Block, Vec<u8>, self::list_storage::DbStorage> {
+	fn get_cache(&mut self, name: CacheKeyId) -> &mut ListCache<Block, Vec<u8>, self::list_storage::DbStorage> {
 		get_cache_helper(
 			&mut self.cache_at,
 			name,
@@ -128,17 +129,17 @@ impl<Block: BlockT> DbCache<Block> {
 // This helper is needed because otherwise the borrow checker will require to
 // clone all parameters outside of the closure.
 fn get_cache_helper<'a, Block: BlockT>(
-	cache_at: &'a mut HashMap<Vec<u8>, ListCache<Block, Vec<u8>, self::list_storage::DbStorage>>,
-	name: Vec<u8>,
+	cache_at: &'a mut HashMap<CacheKeyId, ListCache<Block, Vec<u8>, self::list_storage::DbStorage>>,
+	name: CacheKeyId,
 	db: &Arc<KeyValueDB>,
 	key_lookup: Option<u32>,
 	header: Option<u32>,
 	cache: Option<u32>,
 	best_finalized_block: &ComplexBlockId<Block>,
 ) -> &'a mut ListCache<Block, Vec<u8>, self::list_storage::DbStorage> {
-	cache_at.entry(name.clone()).or_insert_with(|| {
+	cache_at.entry(name).or_insert_with(|| {
 		ListCache::new(
-			self::list_storage::DbStorage::new(name, db.clone(),
+			self::list_storage::DbStorage::new(name.to_vec(), db.clone(),
 				self::list_storage::DbColumns {
 					meta: COLUMN_META,
 					key_lookup,
@@ -154,7 +155,7 @@ fn get_cache_helper<'a, Block: BlockT>(
 
 /// Cache operations that are to be committed after database transaction is committed.
 pub struct DbCacheTransactionOps<Block: BlockT> {
-	cache_at_op: HashMap<Vec<u8>, self::list_cache::CommitOperation<Block, Vec<u8>>>,
+	cache_at_op: HashMap<CacheKeyId, self::list_cache::CommitOperation<Block, Vec<u8>>>,
 	best_finalized_block: Option<ComplexBlockId<Block>>,
 }
 
@@ -162,7 +163,7 @@ pub struct DbCacheTransactionOps<Block: BlockT> {
 pub struct DbCacheTransaction<'a, Block: BlockT> {
 	cache: &'a mut DbCache<Block>,
 	tx: &'a mut DBTransaction,
-	cache_at_op: HashMap<Vec<u8>, self::list_cache::CommitOperation<Block, Vec<u8>>>,
+	cache_at_op: HashMap<CacheKeyId, self::list_cache::CommitOperation<Block, Vec<u8>>>,
 	best_finalized_block: Option<ComplexBlockId<Block>>,
 }
 
@@ -180,7 +181,7 @@ impl<'a, Block: BlockT> DbCacheTransaction<'a, Block> {
 		mut self,
 		parent: ComplexBlockId<Block>,
 		block: ComplexBlockId<Block>,
-		data_at: HashMap<Vec<u8>, Vec<u8>>,
+		data_at: HashMap<CacheKeyId, Vec<u8>>,
 		is_final: bool,
 	) -> ClientResult<Self> {
 		assert!(self.cache_at_op.is_empty());
@@ -192,8 +193,8 @@ impl<'a, Block: BlockT> DbCacheTransaction<'a, Block> {
 			.cloned()
 			.collect::<Vec<_>>();
 
-		let mut insert_op = |name: Vec<u8>, value: Option<Vec<u8>>| -> Result<(), client::error::Error> {
-			let cache = self.cache.get_cache(name.clone());
+		let mut insert_op = |name: CacheKeyId, value: Option<Vec<u8>>| -> Result<(), client::error::Error> {
+			let cache = self.cache.get_cache(name);
 			let op = cache.on_block_insert(
 				&mut self::list_storage::DbStorageTransaction::new(
 					cache.storage(),
@@ -253,7 +254,7 @@ impl<'a, Block: BlockT> DbCacheTransaction<'a, Block> {
 pub struct DbCacheSync<Block: BlockT>(pub RwLock<DbCache<Block>>);
 
 impl<Block: BlockT> BlockchainCache<Block> for DbCacheSync<Block> {
-	fn get_at(&self, key: &[u8], at: &BlockId<Block>) -> Option<Vec<u8>> {
+	fn get_at(&self, key: &CacheKeyId, at: &BlockId<Block>) -> Option<Vec<u8>> {
 		let cache = self.0.read();
 		let storage = cache.cache_at.get(key)?.storage();
 		let db = storage.db();
diff --git a/substrate/core/client/db/src/lib.rs b/substrate/core/client/db/src/lib.rs
index dde01bf929..7657bfd396 100644
--- a/substrate/core/client/db/src/lib.rs
+++ b/substrate/core/client/db/src/lib.rs
@@ -55,6 +55,7 @@ use crate::utils::{Meta, db_err, meta_keys, open_database, read_db, block_id_to_
 use client::leaves::{LeafSet, FinalizationDisplaced};
 use client::children;
 use state_db::StateDb;
+use consensus_common::well_known_cache_keys;
 use crate::storage_cache::{CachingState, SharedCache, new_shared_cache};
 use log::{trace, debug, warn};
 pub use state_db::PruningMode;
@@ -313,7 +314,7 @@ where Block: BlockT<Hash=H256>,
 		Ok(())
 	}
 
-	fn update_cache(&mut self, _cache: HashMap<Vec<u8>, Vec<u8>>) {
+	fn update_cache(&mut self, _cache: HashMap<well_known_cache_keys::Id, Vec<u8>>) {
 		// Currently cache isn't implemented on full nodes.
 	}
 
diff --git a/substrate/core/client/db/src/light.rs b/substrate/core/client/db/src/light.rs
index f064035d51..62b6486f54 100644
--- a/substrate/core/client/db/src/light.rs
+++ b/substrate/core/client/db/src/light.rs
@@ -33,6 +33,7 @@ use primitives::Blake2Hasher;
 use runtime_primitives::generic::BlockId;
 use runtime_primitives::traits::{Block as BlockT, Header as HeaderT,
 	Zero, One, As, NumberFor, Digest, DigestItem};
+use consensus_common::well_known_cache_keys;
 use crate::cache::{DbCacheSync, DbCache, ComplexBlockId};
 use crate::utils::{self, meta_keys, Meta, db_err, open_database,
 	read_db, block_id_to_lookup_key, read_meta};
@@ -370,7 +371,7 @@ impl<Block> LightBlockchainStorage<Block> for LightStorage<Block>
 	fn import_header(
 		&self,
 		header: Block::Header,
-		cache_at: HashMap<Vec<u8>, Vec<u8>>,
+		cache_at: HashMap<well_known_cache_keys::Id, Vec<u8>>,
 		leaf_state: NewBlockState,
 		aux_ops: Vec<(Vec<u8>, Option<Vec<u8>>)>,
 	) -> ClientResult<()> {
@@ -539,7 +540,6 @@ pub(crate) mod tests {
 	use runtime_primitives::generic::DigestItem;
 	use runtime_primitives::testing::{H256 as Hash, Header, Block as RawBlock, ExtrinsicWrapper};
 	use runtime_primitives::traits::AuthorityIdFor;
-	use consensus_common::well_known_cache_keys;
 	use super::*;
 
 	type Block = RawBlock<ExtrinsicWrapper<u32>>;
@@ -569,7 +569,7 @@ pub(crate) mod tests {
 
 	pub fn insert_block<F: Fn() -> Header>(
 		db: &LightStorage<Block>,
-		cache: HashMap<Vec<u8>, Vec<u8>>,
+		cache: HashMap<well_known_cache_keys::Id, Vec<u8>>,
 		header: F,
 	) -> Hash {
 		let header = header();
@@ -580,7 +580,7 @@ pub(crate) mod tests {
 
 	fn insert_final_block<F: Fn() -> Header>(
 		db: &LightStorage<Block>,
-		cache: HashMap<Vec<u8>, Vec<u8>>,
+		cache: HashMap<well_known_cache_keys::Id, Vec<u8>>,
 		header: F,
 	) -> Hash {
 		let header = header();
@@ -591,7 +591,7 @@ pub(crate) mod tests {
 
 	fn insert_non_best_block<F: Fn() -> Header>(
 		db: &LightStorage<Block>,
-		cache: HashMap<Vec<u8>, Vec<u8>>,
+		cache: HashMap<well_known_cache_keys::Id, Vec<u8>>,
 		header: F,
 	) -> Hash {
 		let header = header();
@@ -828,18 +828,18 @@ pub(crate) mod tests {
 			}
 		}
 
-		fn same_authorities() -> HashMap<Vec<u8>, Vec<u8>> {
+		fn same_authorities() -> HashMap<well_known_cache_keys::Id, Vec<u8>> {
 			HashMap::new()
 		}
 
-		fn make_authorities(authorities: Vec<AuthorityId>) -> HashMap<Vec<u8>, Vec<u8>> {
+		fn make_authorities(authorities: Vec<AuthorityId>) -> HashMap<well_known_cache_keys::Id, Vec<u8>> {
 			let mut map = HashMap::new();
-			map.insert(well_known_cache_keys::AUTHORITIES.to_vec(), authorities.encode());
+			map.insert(well_known_cache_keys::AUTHORITIES, authorities.encode());
 			map
 		}
 
 		fn get_authorities(cache: &BlockchainCache<Block>, at: BlockId<Block>) -> Option<Vec<AuthorityId>> {
-			cache.get_at(well_known_cache_keys::AUTHORITIES, &at).and_then(|val| Decode::decode(&mut &val[..]))
+			cache.get_at(&well_known_cache_keys::AUTHORITIES, &at).and_then(|val| Decode::decode(&mut &val[..]))
 		}
 
 		let auth1 = || AuthorityId::from_raw([1u8; 32]);
diff --git a/substrate/core/client/src/backend.rs b/substrate/core/client/src/backend.rs
index 864d04ed61..8a6ffe4384 100644
--- a/substrate/core/client/src/backend.rs
+++ b/substrate/core/client/src/backend.rs
@@ -23,6 +23,7 @@ use runtime_primitives::{generic::BlockId, Justification, StorageOverlay, Childr
 use runtime_primitives::traits::{Block as BlockT, NumberFor};
 use state_machine::backend::Backend as StateBackend;
 use state_machine::ChangesTrieStorage as StateChangesTrieStorage;
+use consensus::well_known_cache_keys;
 use hash_db::Hasher;
 use trie::MemoryDB;
 
@@ -75,7 +76,7 @@ pub trait BlockImportOperation<Block, H> where
 	) -> error::Result<()>;
 
 	/// Update cached data.
-	fn update_cache(&mut self, cache: HashMap<Vec<u8>, Vec<u8>>);
+	fn update_cache(&mut self, cache: HashMap<well_known_cache_keys::Id, Vec<u8>>);
 	/// Inject storage data into the database.
 	fn update_db_storage(&mut self, update: <Self::State as StateBackend<H>>::Transaction) -> error::Result<()>;
 	/// Inject storage data into the database replacing any existing data.
diff --git a/substrate/core/client/src/blockchain.rs b/substrate/core/client/src/blockchain.rs
index 682d686bd5..5d7b2a9c23 100644
--- a/substrate/core/client/src/blockchain.rs
+++ b/substrate/core/client/src/blockchain.rs
@@ -21,6 +21,7 @@ use std::sync::Arc;
 use runtime_primitives::traits::{Block as BlockT, Header as HeaderT, NumberFor};
 use runtime_primitives::generic::BlockId;
 use runtime_primitives::Justification;
+use consensus::well_known_cache_keys;
 
 use crate::error::{ErrorKind, Result};
 
@@ -100,7 +101,7 @@ pub trait ProvideCache<Block: BlockT> {
 /// Blockchain optional data cache.
 pub trait Cache<Block: BlockT>: Send + Sync {
 	/// Returns cached value by the given key.
-	fn get_at(&self, key: &[u8], block: &BlockId<Block>) -> Option<Vec<u8>>;
+	fn get_at(&self, key: &well_known_cache_keys::Id, block: &BlockId<Block>) -> Option<Vec<u8>>;
 }
 
 /// Blockchain info
diff --git a/substrate/core/client/src/client.rs b/substrate/core/client/src/client.rs
index 7ab66cbc09..041933cfff 100644
--- a/substrate/core/client/src/client.rs
+++ b/substrate/core/client/src/client.rs
@@ -27,7 +27,7 @@ use runtime_primitives::{
 };
 use consensus::{
 	Error as ConsensusError, ErrorKind as ConsensusErrorKind, ImportBlock, ImportResult,
-	BlockOrigin, ForkChoiceStrategy,
+	BlockOrigin, ForkChoiceStrategy, well_known_cache_keys::Id as CacheKeyId,
 };
 use runtime_primitives::traits::{
 	Block as BlockT, Header as HeaderT, Zero, As, NumberFor, CurrentHeight, BlockNumberToHash,
@@ -672,7 +672,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 		&self,
 		operation: &mut ClientImportOperation<Block, Blake2Hasher, B>,
 		import_block: ImportBlock<Block>,
-		new_cache: HashMap<Vec<u8>, Vec<u8>>,
+		new_cache: HashMap<CacheKeyId, Vec<u8>>,
 	) -> error::Result<ImportResult> where
 		E: CallExecutor<Block, Blake2Hasher> + Send + Sync + Clone,
 	{
@@ -743,7 +743,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 		import_headers: PrePostHeader<Block::Header>,
 		justification: Option<Justification>,
 		body: Option<Vec<Block::Extrinsic>>,
-		new_cache: HashMap<Vec<u8>, Vec<u8>>,
+		new_cache: HashMap<CacheKeyId, Vec<u8>>,
 		finalized: bool,
 		aux: Vec<(Vec<u8>, Option<Vec<u8>>)>,
 		fork_choice: ForkChoiceStrategy,
@@ -1396,7 +1396,7 @@ impl<B, E, Block, RA> consensus::BlockImport<Block> for Client<B, E, Block, RA>
 	fn import_block(
 		&self,
 		import_block: ImportBlock<Block>,
-		new_cache: HashMap<Vec<u8>, Vec<u8>>,
+		new_cache: HashMap<CacheKeyId, Vec<u8>>,
 	) -> Result<ImportResult, Self::Error> {
 		self.lock_import_and_run(|operation| {
 			self.apply_block(operation, import_block, new_cache)
diff --git a/substrate/core/client/src/in_mem.rs b/substrate/core/client/src/in_mem.rs
index d272135628..29256169f9 100644
--- a/substrate/core/client/src/in_mem.rs
+++ b/substrate/core/client/src/in_mem.rs
@@ -29,6 +29,7 @@ use state_machine::{self, InMemoryChangesTrieStorage, ChangesTrieAnchorBlockId};
 use hash_db::Hasher;
 use heapsize::HeapSizeOf;
 use trie::MemoryDB;
+use consensus::well_known_cache_keys::Id as CacheKeyId;
 
 use crate::error;
 use crate::backend::{self, NewBlockState};
@@ -390,7 +391,7 @@ impl<Block: BlockT> light::blockchain::Storage<Block> for Blockchain<Block>
 	fn import_header(
 		&self,
 		header: Block::Header,
-		_cache: HashMap<Vec<u8>, Vec<u8>>,
+		_cache: HashMap<CacheKeyId, Vec<u8>>,
 		state: NewBlockState,
 		aux_ops: Vec<(Vec<u8>, Option<Vec<u8>>)>,
 	) -> error::Result<()> {
@@ -431,7 +432,7 @@ impl<Block: BlockT> light::blockchain::Storage<Block> for Blockchain<Block>
 /// In-memory operation.
 pub struct BlockImportOperation<Block: BlockT, H: Hasher> {
 	pending_block: Option<PendingBlock<Block>>,
-	pending_cache: HashMap<Vec<u8>, Vec<u8>>,
+	pending_cache: HashMap<CacheKeyId, Vec<u8>>,
 	old_state: InMemory<H>,
 	new_state: Option<InMemory<H>>,
 	changes_trie_update: Option<MemoryDB<H>>,
@@ -468,7 +469,7 @@ where
 		Ok(())
 	}
 
-	fn update_cache(&mut self, cache: HashMap<Vec<u8>, Vec<u8>>) {
+	fn update_cache(&mut self, cache: HashMap<CacheKeyId, Vec<u8>>) {
 		self.pending_cache = cache;
 	}
 
diff --git a/substrate/core/client/src/light/backend.rs b/substrate/core/client/src/light/backend.rs
index c62a89ce9d..b4b805f3c6 100644
--- a/substrate/core/client/src/light/backend.rs
+++ b/substrate/core/client/src/light/backend.rs
@@ -34,6 +34,7 @@ use crate::light::fetcher::{Fetcher, RemoteReadRequest};
 use hash_db::Hasher;
 use trie::MemoryDB;
 use heapsize::HeapSizeOf;
+use consensus::well_known_cache_keys;
 
 const IN_MEMORY_EXPECT_PROOF: &str = "InMemory state backend has Void error type and always suceeds; qed";
 
@@ -46,7 +47,7 @@ pub struct Backend<S, F, H> {
 /// Light block (header and justification) import operation.
 pub struct ImportOperation<Block: BlockT, S, F, H> {
 	header: Option<Block::Header>,
-	cache: HashMap<Vec<u8>, Vec<u8>>,
+	cache: HashMap<well_known_cache_keys::Id, Vec<u8>>,
 	leaf_state: NewBlockState,
 	aux_ops: Vec<(Vec<u8>, Option<Vec<u8>>)>,
 	finalized_blocks: Vec<BlockId<Block>>,
@@ -254,7 +255,7 @@ where
 		Ok(())
 	}
 
-	fn update_cache(&mut self, cache: HashMap<Vec<u8>, Vec<u8>>) {
+	fn update_cache(&mut self, cache: HashMap<well_known_cache_keys::Id, Vec<u8>>) {
 		self.cache = cache;
 	}
 
diff --git a/substrate/core/client/src/light/blockchain.rs b/substrate/core/client/src/light/blockchain.rs
index cf6304253a..e081c14d1a 100644
--- a/substrate/core/client/src/light/blockchain.rs
+++ b/substrate/core/client/src/light/blockchain.rs
@@ -23,6 +23,7 @@ use parking_lot::Mutex;
 
 use runtime_primitives::{Justification, generic::BlockId};
 use runtime_primitives::traits::{Block as BlockT, Header as HeaderT, NumberFor, Zero};
+use consensus::well_known_cache_keys;
 
 use crate::backend::{AuxStore, NewBlockState};
 use crate::blockchain::{Backend as BlockchainBackend, BlockStatus, Cache as BlockchainCache,
@@ -40,7 +41,7 @@ pub trait Storage<Block: BlockT>: AuxStore + BlockchainHeaderBackend<Block> {
 	fn import_header(
 		&self,
 		header: Block::Header,
-		cache: HashMap<Vec<u8>, Vec<u8>>,
+		cache: HashMap<well_known_cache_keys::Id, Vec<u8>>,
 		state: NewBlockState,
 		aux_ops: Vec<(Vec<u8>, Option<Vec<u8>>)>,
 	) -> ClientResult<()>;
@@ -252,7 +253,7 @@ pub mod tests {
 		fn import_header(
 			&self,
 			_header: Header,
-			_cache: HashMap<Vec<u8>, Vec<u8>>,
+			_cache: HashMap<well_known_cache_keys::Id, Vec<u8>>,
 			_state: NewBlockState,
 			_aux_ops: Vec<(Vec<u8>, Option<Vec<u8>>)>,
 		) -> ClientResult<()> {
diff --git a/substrate/core/consensus/aura/src/lib.rs b/substrate/core/consensus/aura/src/lib.rs
index d3ea731795..fd33228b66 100644
--- a/substrate/core/consensus/aura/src/lib.rs
+++ b/substrate/core/consensus/aura/src/lib.rs
@@ -694,7 +694,7 @@ fn authorities<B, C>(client: &C, at: &BlockId<B>) -> Result<Vec<AuthorityIdFor<B
 {
 	client
 		.cache()
-		.and_then(|cache| cache.get_at(well_known_cache_keys::AUTHORITIES, at)
+		.and_then(|cache| cache.get_at(&well_known_cache_keys::AUTHORITIES, at)
 			.and_then(|v| Decode::decode(&mut &v[..])))
 		.or_else(|| client.runtime_api().authorities(at).ok())
 		.ok_or_else(|| consensus_common::ErrorKind::InvalidAuthoritiesSet.into())
diff --git a/substrate/core/consensus/common/src/block_import.rs b/substrate/core/consensus/common/src/block_import.rs
index a4a765da4e..7debe1acfe 100644
--- a/substrate/core/consensus/common/src/block_import.rs
+++ b/substrate/core/consensus/common/src/block_import.rs
@@ -20,6 +20,7 @@ use runtime_primitives::traits::{Block as BlockT, DigestItemFor, Header as Heade
 use runtime_primitives::Justification;
 use std::borrow::Cow;
 use std::collections::HashMap;
+use crate::well_known_cache_keys;
 
 /// Block import result.
 #[derive(Debug, PartialEq, Eq)]
@@ -182,7 +183,7 @@ pub trait BlockImport<B: BlockT> {
 	fn import_block(
 		&self,
 		block: ImportBlock<B>,
-		cache: HashMap<Vec<u8>, Vec<u8>>,
+		cache: HashMap<well_known_cache_keys::Id, Vec<u8>>,
 	) -> Result<ImportResult, Self::Error>;
 }
 
diff --git a/substrate/core/consensus/common/src/import_queue.rs b/substrate/core/consensus/common/src/import_queue.rs
index 1d0a52d324..7a418ae9f4 100644
--- a/substrate/core/consensus/common/src/import_queue.rs
+++ b/substrate/core/consensus/common/src/import_queue.rs
@@ -570,7 +570,7 @@ pub fn import_single_block<B: BlockT, V: Verifier<B>>(
 
 	let mut cache = HashMap::new();
 	if let Some(authorities) = new_authorities {
-		cache.insert(crate::well_known_cache_keys::AUTHORITIES.to_vec(), authorities.encode());
+		cache.insert(crate::well_known_cache_keys::AUTHORITIES, authorities.encode());
 	}
 
 	import_error(import_handle.import_block(import_block, cache))
diff --git a/substrate/core/consensus/common/src/lib.rs b/substrate/core/consensus/common/src/lib.rs
index c1308f2da9..134a34454e 100644
--- a/substrate/core/consensus/common/src/lib.rs
+++ b/substrate/core/consensus/common/src/lib.rs
@@ -120,6 +120,9 @@ impl<T: SyncOracle> SyncOracle for Arc<T> {
 
 /// A list of all well known keys in the cache.
 pub mod well_known_cache_keys {
+	/// The type representing cache keys.
+	pub type Id = [u8; 4];
+
 	/// A list of authorities.
-	pub const AUTHORITIES: &'static [u8] = b"auth";
+	pub const AUTHORITIES: Id = *b"auth";
 }
diff --git a/substrate/core/finality-grandpa/src/import.rs b/substrate/core/finality-grandpa/src/import.rs
index 7914660e29..5fa20fc2f6 100644
--- a/substrate/core/finality-grandpa/src/import.rs
+++ b/substrate/core/finality-grandpa/src/import.rs
@@ -27,7 +27,7 @@ use client::backend::Backend;
 use client::runtime_api::ApiExt;
 use consensus_common::{
 	BlockImport, Error as ConsensusError, ErrorKind as ConsensusErrorKind,
-	ImportBlock, ImportResult, JustificationImport,
+	ImportBlock, ImportResult, JustificationImport, well_known_cache_keys,
 };
 use fg_primitives::GrandpaApi;
 use runtime_primitives::Justification;
@@ -388,7 +388,7 @@ impl<B, E, Block: BlockT<Hash=H256>, RA, PRA> BlockImport<Block>
 {
 	type Error = ConsensusError;
 
-	fn import_block(&self, mut block: ImportBlock<Block>, new_cache: HashMap<Vec<u8>, Vec<u8>>)
+	fn import_block(&self, mut block: ImportBlock<Block>, new_cache: HashMap<well_known_cache_keys::Id, Vec<u8>>)
 		-> Result<ImportResult, Self::Error>
 	{
 		let hash = block.post_header().hash();