diff --git a/configs/constant_presets/mainnet.yaml b/configs/constant_presets/mainnet.yaml
index 629badcee..269e96b23 100644
--- a/configs/constant_presets/mainnet.yaml
+++ b/configs/constant_presets/mainnet.yaml
@@ -117,9 +117,9 @@ MAX_TRANSFERS: 0
 
 # Signature domains
 # ---------------------------------------------------------------
-DOMAIN_BEACON_PROPOSER: 0
-DOMAIN_RANDAO: 1
-DOMAIN_ATTESTATION: 2
-DOMAIN_DEPOSIT: 3
-DOMAIN_VOLUNTARY_EXIT: 4
-DOMAIN_TRANSFER: 5
+DOMAIN_BEACON_PROPOSER: 0x00000000
+DOMAIN_RANDAO: 0x01000000
+DOMAIN_ATTESTATION: 0x02000000
+DOMAIN_DEPOSIT: 0x03000000
+DOMAIN_VOLUNTARY_EXIT: 0x04000000
+DOMAIN_TRANSFER: 0x05000000
diff --git a/configs/constant_presets/minimal.yaml b/configs/constant_presets/minimal.yaml
index 1d0ad015d..d0fb988b8 100644
--- a/configs/constant_presets/minimal.yaml
+++ b/configs/constant_presets/minimal.yaml
@@ -118,9 +118,9 @@ MAX_TRANSFERS: 0
 
 # Signature domains
 # ---------------------------------------------------------------
-DOMAIN_BEACON_PROPOSER: 0
-DOMAIN_RANDAO: 1
-DOMAIN_ATTESTATION: 2
-DOMAIN_DEPOSIT: 3
-DOMAIN_VOLUNTARY_EXIT: 4
-DOMAIN_TRANSFER: 5
+DOMAIN_BEACON_PROPOSER: 0x00000000
+DOMAIN_RANDAO: 0x01000000
+DOMAIN_ATTESTATION: 0x02000000
+DOMAIN_DEPOSIT: 0x03000000
+DOMAIN_VOLUNTARY_EXIT: 0x04000000
+DOMAIN_TRANSFER: 0x05000000
\ No newline at end of file
diff --git a/scripts/build_spec.py b/scripts/build_spec.py
index 1542973f2..d5b0c9aaf 100644
--- a/scripts/build_spec.py
+++ b/scripts/build_spec.py
@@ -25,7 +25,7 @@ from eth2spec.utils.ssz.ssz_impl import (
 )
 from eth2spec.utils.ssz.ssz_typing import (
     bit, boolean, Container, List, Vector, uint64,
-    Bytes4, Bytes32, Bytes48, Bytes96, Bitlist, Bitvector,
+    Bytes4, Bytes8, Bytes32, Bytes48, Bytes96, Bitlist, Bitvector,
 )
 from eth2spec.utils.bls import (
     bls_aggregate_pubkeys,
@@ -52,7 +52,7 @@ from eth2spec.utils.ssz.ssz_impl import (
 )
 from eth2spec.utils.ssz.ssz_typing import (
     bit, boolean, Container, List, Vector, Bytes, uint64,
-    Bytes4, Bytes32, Bytes48, Bytes96, Bitlist, Bitvector,
+    Bytes4, Bytes8, Bytes32, Bytes48, Bytes96, Bitlist, Bitvector,
 )
 from eth2spec.utils.bls import (
     bls_aggregate_pubkeys,
@@ -94,7 +94,10 @@ def compute_committee(indices: Sequence[ValidatorIndex],  # type: ignore
 def apply_constants_preset(preset: Dict[str, Any]) -> None:
     global_vars = globals()
     for k, v in preset.items():
-        global_vars[k] = v
+        if k.startswith('DOMAIN_'):
+            global_vars[k] = DomainType(v)  # domain types are defined as bytes in the configs
+        else:
+            global_vars[k] = v
 
     # Deal with derived constants
     global_vars['GENESIS_EPOCH'] = slot_to_epoch(GENESIS_SLOT)
@@ -135,6 +138,9 @@ def objects_to_spec(functions: Dict[str, str],
         )
     )
     functions_spec = '\n\n'.join(functions.values())
+    for k in list(constants.keys()):
+        if k.startswith('DOMAIN_'):
+            constants[k] = f"DomainType(({constants[k]}).to_bytes(length=4, byteorder='little'))"
     constants_spec = '\n'.join(map(lambda x: '%s = %s' % (x, constants[x]), constants))
     ssz_objects_instantiation_spec = '\n\n'.join(ssz_objects.values())
     ssz_objects_reinitialization_spec = (
diff --git a/specs/bls_signature.md b/specs/bls_signature.md
index b901b9345..652279cd7 100644
--- a/specs/bls_signature.md
+++ b/specs/bls_signature.md
@@ -71,10 +71,10 @@ We require:
 G2_cofactor = 305502333931268344200999753193121504214466019254188142667664032982267604182971884026507427359259977847832272839041616661285803823378372096355777062779109
 q = 4002409555221667393417789825735904156556882819939007885332058136124031650490837864442687629129015664037894272559787
 
-def hash_to_G2(message_hash: Bytes32, domain: uint64) -> Tuple[uint384, uint384]:
+def hash_to_G2(message_hash: Bytes32, domain: Bytes8) -> Tuple[uint384, uint384]:
     # Initial candidate x coordinate
-    x_re = int.from_bytes(hash(message_hash + bytes8(domain) + b'\x01'), 'big')
-    x_im = int.from_bytes(hash(message_hash + bytes8(domain) + b'\x02'), 'big')
+    x_re = int.from_bytes(hash(message_hash + domain + b'\x01'), 'big')
+    x_im = int.from_bytes(hash(message_hash + domain + b'\x02'), 'big')
     x_coordinate = Fq2([x_re, x_im])  # x = x_re + i * x_im
     
     # Test candidate y coordinates until a one is found
@@ -130,7 +130,7 @@ g = Fq2([g_x, g_y])
 
 ### `bls_verify`
 
-Let `bls_verify(pubkey: Bytes48, message_hash: Bytes32, signature: Bytes96, domain: uint64) -> bool`:
+Let `bls_verify(pubkey: Bytes48, message_hash: Bytes32, signature: Bytes96, domain: Bytes8) -> bool`:
 
 * Verify that `pubkey` is a valid G1 point.
 * Verify that `signature` is a valid G2 point.
@@ -138,7 +138,7 @@ Let `bls_verify(pubkey: Bytes48, message_hash: Bytes32, signature: Bytes96, doma
 
 ### `bls_verify_multiple`
 
-Let `bls_verify_multiple(pubkeys: List[Bytes48], message_hashes: List[Bytes32], signature: Bytes96, domain: uint64) -> bool`:
+Let `bls_verify_multiple(pubkeys: List[Bytes48], message_hashes: List[Bytes32], signature: Bytes96, domain: Bytes8) -> bool`:
 
 * Verify that each `pubkey` in `pubkeys` is a valid G1 point.
 * Verify that `signature` is a valid G2 point.
diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 7dd6a71bf..3918fda06 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -147,6 +147,8 @@ We define the following Python custom types for type hinting and readability:
 | `ValidatorIndex` | `uint64` | a validator registry index |
 | `Gwei` | `uint64` | an amount in Gwei |
 | `Version` | `Bytes4` | a fork version number |
+| `DomainType` | `Bytes4` | a signature domain type |
+| `Domain` | `Bytes8` | a signature domain |
 | `Hash` | `Bytes32` | a hash |
 | `BLSPubkey` | `Bytes48` | a BLS12-381 public key |
 | `BLSSignature` | `Bytes96` | a BLS12-381 signature |
@@ -249,7 +251,9 @@ The following values are (non-configurable) constants used throughout the specif
 | `MAX_VOLUNTARY_EXITS` | `2**4` (= 16) |
 | `MAX_TRANSFERS` | `0` |
 
-### Signature domains
+### Signature domain types
+
+The following types are defined, mapping into `DomainType` (little endian):
 
 | Name | Value |
 | - | - |
@@ -767,11 +771,11 @@ def compute_activation_exit_epoch(epoch: Epoch) -> Epoch:
 #### `bls_domain`
 
 ```python
-def bls_domain(domain_type: uint64, fork_version: bytes=b'\x00' * 4) -> int:
+def bls_domain(domain_type: DomainType, fork_version: bytes=b'\x00' * 4) -> Domain:
     """
     Return the BLS domain for the ``domain_type`` and ``fork_version``.
     """
-    return bytes_to_int(int_to_bytes(domain_type, length=4) + fork_version)
+    return Domain(domain_type + fork_version)
 ```
 
 ### Beacon state accessors
@@ -997,7 +1001,7 @@ def get_total_active_balance(state: BeaconState) -> Gwei:
 #### `get_domain`
 
 ```python
-def get_domain(state: BeaconState, domain_type: uint64, message_epoch: Epoch=None) -> int:
+def get_domain(state: BeaconState, domain_type: DomainType, message_epoch: Epoch=None) -> Domain:
     """
     Return the signature domain (fork version concatenated with domain type) of a message.
     """
diff --git a/specs/core/1_custody-game.md b/specs/core/1_custody-game.md
index babe4f991..cdca249d9 100644
--- a/specs/core/1_custody-game.md
+++ b/specs/core/1_custody-game.md
@@ -107,7 +107,9 @@ This document details the beacon chain additions and changes in Phase 1 of Ether
 | - | - |
 | `EARLY_DERIVED_SECRET_REVEAL_SLOT_REWARD_MULTIPLE` | `2**1` (= 2) |
 
-### Signature domains
+### Signature domain types
+
+The following types are defined, mapping into `DomainType` (little endian):
 
 | Name | Value |
 | - | - |
diff --git a/specs/core/1_shard-data-chains.md b/specs/core/1_shard-data-chains.md
index 745d437c2..e212c97a5 100644
--- a/specs/core/1_shard-data-chains.md
+++ b/specs/core/1_shard-data-chains.md
@@ -62,7 +62,9 @@ This document describes the shard data layer and the shard fork choice rule in P
 | `CROSSLINK_LOOKBACK` | `2**0` (= 1) | epochs  | 6.2 minutes |
 | `PERSISTENT_COMMITTEE_PERIOD` | `2**11` (= 2,048) | epochs | ~9 days |
 
-### Signature domains
+### Signature domain types
+
+The following types are defined, mapping into `DomainType` (little endian):
 
 | Name | Value |
 | - | - |
diff --git a/test_libs/pyspec/eth2spec/utils/bls.py b/test_libs/pyspec/eth2spec/utils/bls.py
index 52f1fed63..b68745866 100644
--- a/test_libs/pyspec/eth2spec/utils/bls.py
+++ b/test_libs/pyspec/eth2spec/utils/bls.py
@@ -23,7 +23,8 @@ def only_with_bls(alt_return=None):
 
 @only_with_bls(alt_return=True)
 def bls_verify(pubkey, message_hash, signature, domain):
-    return bls.verify(message_hash=message_hash, pubkey=pubkey, signature=signature, domain=domain)
+    return bls.verify(message_hash=message_hash, pubkey=pubkey,
+                      signature=signature, domain=int.from_bytes(domain, byteorder='little'))
 
 
 @only_with_bls(alt_return=True)
@@ -43,4 +44,5 @@ def bls_aggregate_signatures(signatures):
 
 @only_with_bls(alt_return=STUB_SIGNATURE)
 def bls_sign(message_hash, privkey, domain):
-    return bls.sign(message_hash=message_hash, privkey=privkey, domain=domain)
+    return bls.sign(message_hash=message_hash, privkey=privkey,
+                    domain=int.from_bytes(domain, byteorder='little'))
diff --git a/test_libs/pyspec/eth2spec/utils/ssz/ssz_typing.py b/test_libs/pyspec/eth2spec/utils/ssz/ssz_typing.py
index d87a22399..7b5798529 100644
--- a/test_libs/pyspec/eth2spec/utils/ssz/ssz_typing.py
+++ b/test_libs/pyspec/eth2spec/utils/ssz/ssz_typing.py
@@ -497,6 +497,11 @@ class BytesN(BaseBytes):
 
 # Helpers for common BytesN types.
 Bytes4: BytesType = BytesN[4]
+Bytes8: BytesType = BytesN[8]
 Bytes32: BytesType = BytesN[32]
 Bytes48: BytesType = BytesN[48]
 Bytes96: BytesType = BytesN[96]
+
+
+class DomainType(Bytes4):
+    pass