diff --git a/WORKSPACE b/WORKSPACE
index 3b0dbb7f8388..b980b97f4b84 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -160,8 +160,8 @@ filegroup(
     visibility = ["//visibility:public"],
 )
     """,
-    sha256 = "f3ff68508dfe9696f23506daf0ca895cda955e30398741e00cffa33a01b0565c",
-    url = "https://github.com/ethereum/eth2.0-spec-tests/releases/download/v0.9.0/mainnet.tar.gz",
+    sha256 = "2608d9085ca98d2b7b51a31ff368fb8c17a094ee02bb0e93884b953290d3fb4b",
+    url = "https://github.com/ethereum/eth2.0-spec-tests/releases/download/v0.9.1/mainnet.tar.gz",
 )
 
 http_archive(
diff --git a/beacon-chain/core/blocks/block_operations.go b/beacon-chain/core/blocks/block_operations.go
index 7a081af47c1c..0587cb818043 100644
--- a/beacon-chain/core/blocks/block_operations.go
+++ b/beacon-chain/core/blocks/block_operations.go
@@ -678,6 +678,13 @@ func VerifyIndexedAttestation(ctx context.Context, beaconState *pb.BeaconState,
 		return fmt.Errorf("validator indices count exceeds MAX_VALIDATORS_PER_COMMITTEE, %d > %d", len(indices), params.BeaconConfig().MaxValidatorsPerCommittee)
 	}
 
+	sorted := sort.SliceIsSorted(indices, func(i, j int) bool {
+		return indices[i] < indices[j]
+	})
+	if !sorted {
+		return fmt.Errorf("attesting indices are not sorted, got %v", sorted)
+	}
+
 	domain := helpers.Domain(beaconState.Fork, indexedAtt.Data.Target.Epoch, params.BeaconConfig().DomainBeaconAttester)
 	var pubkey *bls.PublicKey
 	var err error
@@ -705,7 +712,8 @@ func VerifyIndexedAttestation(ctx context.Context, beaconState *pb.BeaconState,
 		return errors.Wrap(err, "could not convert bytes to signature")
 	}
 
-	if !sig.Verify(messageHash[:], pubkey, domain) {
+	voted := len(indices) > 0
+	if voted && !sig.Verify(messageHash[:], pubkey, domain) {
 		return fmt.Errorf("attestation aggregation signature did not verify")
 	}
 	return nil
diff --git a/beacon-chain/core/blocks/spectest/attestation_mainnet_test.go b/beacon-chain/core/blocks/spectest/attestation_mainnet_test.go
index d4c551eaa674..7bae9a8b5b15 100644
--- a/beacon-chain/core/blocks/spectest/attestation_mainnet_test.go
+++ b/beacon-chain/core/blocks/spectest/attestation_mainnet_test.go
@@ -5,6 +5,5 @@ import (
 )
 
 func TestAttestationMainnet(t *testing.T) {
-	t.Skip("Skip until 3960 merges")
 	runAttestationTest(t, "mainnet")
 }
diff --git a/beacon-chain/core/blocks/spectest/attester_slashing_mainnet_test.go b/beacon-chain/core/blocks/spectest/attester_slashing_mainnet_test.go
index d8ff2cf7d334..f6064a96e31e 100644
--- a/beacon-chain/core/blocks/spectest/attester_slashing_mainnet_test.go
+++ b/beacon-chain/core/blocks/spectest/attester_slashing_mainnet_test.go
@@ -5,6 +5,5 @@ import (
 )
 
 func TestAttesterSlashingMainnet(t *testing.T) {
-	t.Skip("Skip until 3960 merges")
 	runAttesterSlashingTest(t, "mainnet")
 }
diff --git a/beacon-chain/core/blocks/spectest/block_processing_mainnet_test.go b/beacon-chain/core/blocks/spectest/block_processing_mainnet_test.go
index 9df9c4823769..e64d83a6cc44 100644
--- a/beacon-chain/core/blocks/spectest/block_processing_mainnet_test.go
+++ b/beacon-chain/core/blocks/spectest/block_processing_mainnet_test.go
@@ -5,6 +5,5 @@ import (
 )
 
 func TestBlockProcessingMainnetYaml(t *testing.T) {
-	t.Skip("Skip until 3960 merges")
 	runBlockProcessingTest(t, "mainnet")
 }
diff --git a/proto/testing/ssz_static_mainnet_test.go b/proto/testing/ssz_static_mainnet_test.go
index b00c926712ed..584a7370f9be 100644
--- a/proto/testing/ssz_static_mainnet_test.go
+++ b/proto/testing/ssz_static_mainnet_test.go
@@ -5,6 +5,5 @@ import (
 )
 
 func TestSZZStatic_Mainnet(t *testing.T) {
-	t.Skip("Skip until 3960 merges")
 	runSSZStaticTests(t, "mainnet")
 }