diff --git a/beacon_node/beacon_chain/test_harness/src/bin.rs b/beacon_node/beacon_chain/test_harness/src/bin.rs
index 216e03d9f4..fa5aa45a25 100644
--- a/beacon_node/beacon_chain/test_harness/src/bin.rs
+++ b/beacon_node/beacon_chain/test_harness/src/bin.rs
@@ -7,6 +7,7 @@ use env_logger::{Builder, Env};
 use log::{info, warn};
 use ssz::TreeHash;
 use std::{fs::File, io::prelude::*};
+use types::attester_slashing::AttesterSlashingBuilder;
 use types::*;
 use yaml_rust::{Yaml, YamlLoader};
 
@@ -195,82 +196,17 @@ fn build_double_vote_attester_slashing(
     harness: &BeaconChainHarness,
     validator_indices: &[u64],
 ) -> AttesterSlashing {
-    let double_voted_slot = Slot::new(0);
-    let shard = 0;
-    let justified_epoch = Epoch::new(0);
-    let epoch = Epoch::new(0);
-    let hash_1 = Hash256::from("1".as_bytes());
-    let hash_2 = Hash256::from("2".as_bytes());
-
-    let mut slashable_attestation_1 = SlashableAttestation {
-        validator_indices: validator_indices.to_vec(),
-        data: AttestationData {
-            slot: double_voted_slot,
-            shard,
-            beacon_block_root: hash_1,
-            epoch_boundary_root: hash_1,
-            shard_block_root: hash_1,
-            latest_crosslink: Crosslink {
-                epoch,
-                shard_block_root: hash_1,
-            },
-            justified_epoch,
-            justified_block_root: hash_1,
-        },
-        custody_bitfield: Bitfield::new(),
-        aggregate_signature: AggregateSignature::new(),
+    let signer = |validator_index: u64, message: &[u8], epoch: Epoch, domain: u64| {
+        harness
+            .validator_sign(validator_index as usize, message, epoch, domain)
+            .expect("Unable to sign AttesterSlashing")
     };
 
-    let mut slashable_attestation_2 = SlashableAttestation {
-        validator_indices: validator_indices.to_vec(),
-        data: AttestationData {
-            slot: double_voted_slot,
-            shard,
-            beacon_block_root: hash_2,
-            epoch_boundary_root: hash_2,
-            shard_block_root: hash_2,
-            latest_crosslink: Crosslink {
-                epoch,
-                shard_block_root: hash_2,
-            },
-            justified_epoch,
-            justified_block_root: hash_2,
-        },
-        custody_bitfield: Bitfield::new(),
-        aggregate_signature: AggregateSignature::new(),
-    };
-
-    let add_signatures = |attestation: &mut SlashableAttestation| {
-        for (i, validator_index) in validator_indices.iter().enumerate() {
-            let attestation_data_and_custody_bit = AttestationDataAndCustodyBit {
-                data: attestation.data.clone(),
-                custody_bit: attestation.custody_bitfield.get(i).unwrap(),
-            };
-            let message = attestation_data_and_custody_bit.hash_tree_root();
-            let signature = harness
-                .validator_sign(
-                    *validator_index as usize,
-                    &message[..],
-                    epoch,
-                    harness.spec.domain_attestation,
-                )
-                .expect("Unable to sign attestation with unknown validator index.");
-            attestation.aggregate_signature.add(&signature);
-        }
-    };
-
-    add_signatures(&mut slashable_attestation_1);
-    add_signatures(&mut slashable_attestation_2);
-
-    AttesterSlashing {
-        slashable_attestation_1,
-        slashable_attestation_2,
-    }
+    AttesterSlashingBuilder::double_vote(validator_indices, signer, &harness.spec)
 }
 
 pub type DepositTuple = (u64, Deposit, Keypair);
 pub type ProposerSlashingTuple = (u64, ProposerSlashing);
-// (slot, validator_indices)
 pub type AttesterSlashingTuple = (u64, Vec<u64>);
 
 struct ExecutionResult {
diff --git a/eth2/types/src/attester_slashing.rs b/eth2/types/src/attester_slashing.rs
index 9cb2123249..ac75a25626 100644
--- a/eth2/types/src/attester_slashing.rs
+++ b/eth2/types/src/attester_slashing.rs
@@ -1,9 +1,13 @@
-use crate::{test_utils::TestRandom, ChainSpec, SlashableAttestation};
+use crate::{test_utils::TestRandom, SlashableAttestation};
 use rand::RngCore;
 use serde_derive::Serialize;
 use ssz_derive::{Decode, Encode, TreeHash};
 use test_random_derive::TestRandom;
 
+mod builder;
+
+pub use builder::AttesterSlashingBuilder;
+
 #[derive(Debug, PartialEq, Clone, Serialize, Encode, Decode, TreeHash, TestRandom)]
 pub struct AttesterSlashing {
     pub slashable_attestation_1: SlashableAttestation,
diff --git a/eth2/types/src/attester_slashing/builder.rs b/eth2/types/src/attester_slashing/builder.rs
new file mode 100644
index 0000000000..d382cb64c2
--- /dev/null
+++ b/eth2/types/src/attester_slashing/builder.rs
@@ -0,0 +1,85 @@
+use crate::*;
+use ssz::TreeHash;
+
+pub struct AttesterSlashingBuilder();
+
+impl AttesterSlashingBuilder {
+    pub fn double_vote<F>(
+        validator_indices: &[u64],
+        signer: F,
+        spec: &ChainSpec,
+    ) -> AttesterSlashing
+    where
+        F: Fn(u64, &[u8], Epoch, u64) -> Signature,
+    {
+        let double_voted_slot = Slot::new(0);
+        let shard = 0;
+        let justified_epoch = Epoch::new(0);
+        let epoch = Epoch::new(0);
+        let hash_1 = Hash256::from("1".as_bytes());
+        let hash_2 = Hash256::from("2".as_bytes());
+
+        let mut slashable_attestation_1 = SlashableAttestation {
+            validator_indices: validator_indices.to_vec(),
+            data: AttestationData {
+                slot: double_voted_slot,
+                shard,
+                beacon_block_root: hash_1,
+                epoch_boundary_root: hash_1,
+                shard_block_root: hash_1,
+                latest_crosslink: Crosslink {
+                    epoch,
+                    shard_block_root: hash_1,
+                },
+                justified_epoch,
+                justified_block_root: hash_1,
+            },
+            custody_bitfield: Bitfield::new(),
+            aggregate_signature: AggregateSignature::new(),
+        };
+
+        let mut slashable_attestation_2 = SlashableAttestation {
+            validator_indices: validator_indices.to_vec(),
+            data: AttestationData {
+                slot: double_voted_slot,
+                shard,
+                beacon_block_root: hash_2,
+                epoch_boundary_root: hash_2,
+                shard_block_root: hash_2,
+                latest_crosslink: Crosslink {
+                    epoch,
+                    shard_block_root: hash_2,
+                },
+                justified_epoch,
+                justified_block_root: hash_2,
+            },
+            custody_bitfield: Bitfield::new(),
+            aggregate_signature: AggregateSignature::new(),
+        };
+
+        let add_signatures = |attestation: &mut SlashableAttestation| {
+            for (i, validator_index) in validator_indices.iter().enumerate() {
+                let attestation_data_and_custody_bit = AttestationDataAndCustodyBit {
+                    data: attestation.data.clone(),
+                    custody_bit: attestation.custody_bitfield.get(i).unwrap(),
+                };
+                let message = attestation_data_and_custody_bit.hash_tree_root();
+                let signature = signer(
+                    *validator_index,
+                    &message[..],
+                    epoch,
+                    spec.domain_attestation,
+                );
+                attestation.aggregate_signature.add(&signature);
+            }
+        };
+
+        add_signatures(&mut slashable_attestation_1);
+        add_signatures(&mut slashable_attestation_2);
+
+        AttesterSlashing {
+            slashable_attestation_1,
+            slashable_attestation_2,
+        }
+    }
+}