diff --git a/core/block_validator_test.go b/core/block_validator_test.go
index 8ee925211..aeb25b0a2 100644
--- a/core/block_validator_test.go
+++ b/core/block_validator_test.go
@@ -51,6 +51,31 @@ func testChainConfig() *ChainConfig {
 					},
 				},
 			},
+			{
+				Name:  "Diehard",
+				Block: big.NewInt(5),
+				Features: []*ForkFeature{
+					{
+						ID: "eip155",
+						Options: ChainFeatureConfigOptions{
+							"chainID": 62,
+						},
+					},
+					{ // ecip1010 bomb delay
+						ID: "gastable",
+						Options: ChainFeatureConfigOptions{
+							"type": "eip160",
+						},
+					},
+					{ // ecip1010 bomb delay
+						ID: "difficulty",
+						Options: ChainFeatureConfigOptions{
+							"type":   "ecip1010",
+							"length": 2000000,
+						},
+					},
+				},
+			},
 		},
 	}
 }
diff --git a/core/config_test.go b/core/config_test.go
index 4acecdcbc..b6b5cf518 100644
--- a/core/config_test.go
+++ b/core/config_test.go
@@ -292,6 +292,7 @@ func TestChainConfig_GetFeature4_WorkForHighNumbers(t *testing.T) {
 }
 
 func TestChainConfig_GetChainID(t *testing.T) {
+	// Test default hardcoded configs.
 	if DefaultConfig.GetChainID().Cmp(DefaultChainConfigChainID) != 0 {
 		t.Error("got: %v, want: %v", DefaultConfig.GetChainID(), DefaultTestnetChainConfigChainID)
 	}
@@ -299,17 +300,31 @@ func TestChainConfig_GetChainID(t *testing.T) {
 		t.Error("got: %v, want: %v", TestConfig.GetChainID(), DefaultTestnetChainConfigChainID)
 	}
 
-	// Test parsing default external config.
-	p, e := filepath.Abs("../cmd/geth/config/mainnet.json")
-	if e != nil {
-		t.Errorf("filepath err: %v", e)
+	// If no chainID (config is empty) returns 0.
+	c := &ChainConfig{}
+	cid := c.GetChainID()
+	// check is zero
+	if cid.Cmp(new(big.Int)) != 0 {
+		t.Errorf("got: %v, want: %v", cid, new(big.Int))
 	}
-	extConfig, err := ReadExternalChainConfig(p)
-	if err != nil {
-		t.Errorf("could not find file: %v", err)
+
+	// Test parsing default external mainnet config.
+	cases := map[string]*big.Int{
+		"../cmd/geth/config/mainnet.json": DefaultChainConfigChainID,
+		"../cmd/geth/config/testnet.json": DefaultTestnetChainConfigChainID,
 	}
-	if extConfig.ChainConfig.GetChainID().Cmp(big.NewInt(61)) != 0 {
-		t.Error("found 0 chainid for eip155")
+	for extConfigPath, wantInt := range cases {
+		p, e := filepath.Abs(extConfigPath)
+		if e != nil {
+			t.Errorf("filepath err: %v", e)
+		}
+		extConfig, err := ReadExternalChainConfig(p)
+		if err != nil {
+			t.Errorf("could not find file: %v", err)
+		}
+		if extConfig.ChainConfig.GetChainID().Cmp(wantInt) != 0 {
+			t.Error("got: %v, want: %v", extConfig.ChainConfig.GetChainID(), wantInt)
+		}
 	}
 }
 
diff --git a/core/types/transaction_signing.go b/core/types/transaction_signing.go
index 2b79ad5e9..f3c672607 100644
--- a/core/types/transaction_signing.go
+++ b/core/types/transaction_signing.go
@@ -134,7 +134,14 @@ func NewChainIdSigner(chainId *big.Int) ChainIdSigner {
 
 func (s ChainIdSigner) Equal(s2 Signer) bool {
 	other, ok := s2.(ChainIdSigner)
-	return ok && other.chainId.Cmp(s.chainId) == 0
+	if !ok {
+		return false
+	}
+	if other.chainId == nil || s.chainId == nil {
+		return false
+	}
+
+	return other.chainId.Cmp(s.chainId) == 0
 }
 
 func (s ChainIdSigner) SignECDSA(tx *Transaction, prv *ecdsa.PrivateKey) (*Transaction, error) {
diff --git a/core/types/transaction_signing_test.go b/core/types/transaction_signing_test.go
index eaf1d345d..4a6f92f08 100644
--- a/core/types/transaction_signing_test.go
+++ b/core/types/transaction_signing_test.go
@@ -135,3 +135,28 @@ func TestCompatibleSign(t *testing.T) {
 		t.Errorf("Incorrect pubkey for Basic Signer:\n%v\n%v", common.ToHex(pub), common.ToHex(pub_tx2))
 	}
 }
+
+func TestChainIdSigner_Equal(t *testing.T) {
+
+	defaultChainID := big.NewInt(61)
+
+	s := NewChainIdSigner(defaultChainID)
+	if s.chainId == nil || s.chainId.Cmp(new(big.Int)) == 0 || s.chainId.Cmp(big.NewInt(0)) == 0 || s.chainId.Cmp(defaultChainID) != 0 {
+		t.Errorf("unexpected: %v", s)
+	}
+
+	s2Invalid0 := NewChainIdSigner(new(big.Int))
+	if s.Equal(s2Invalid0) {
+		t.Errorf("unexpected: s: %v, s2: %v", s, s2Invalid0)
+	}
+
+	s262 := NewChainIdSigner(big.NewInt(62))
+	if s.Equal(s262) {
+		t.Errorf("unexpected: s: %v, s2: %v", s, s262)
+	}
+
+	s261 := NewChainIdSigner(defaultChainID)
+	if !s.Equal(s261) {
+		t.Errorf("unexpected: s: %v, s2: %v", s, s261)
+	}
+}