diff --git a/EthereumKit/Classes/Api/Core/RpcBlockchain.swift b/EthereumKit/Classes/Api/Core/RpcBlockchain.swift
index a3c8385e..6db34458 100644
--- a/EthereumKit/Classes/Api/Core/RpcBlockchain.swift
+++ b/EthereumKit/Classes/Api/Core/RpcBlockchain.swift
@@ -162,7 +162,7 @@ extension RpcBlockchain: IBlockchain {
         syncer.single(rpc: CallJsonRpc(contractAddress: contractAddress, data: data, defaultBlockParameter: defaultBlockParameter))
     }
 
-    func estimateGas(to: Address, amount: BigUInt?, gasLimit: Int?, gasPrice: Int?, data: Data?) -> Single<Int> {
+    func estimateGas(to: Address?, amount: BigUInt?, gasLimit: Int?, gasPrice: Int?, data: Data?) -> Single<Int> {
         syncer.single(rpc: EstimateGasJsonRpc(from: address, to: to, amount: amount, gasLimit: gasLimit, gasPrice: gasPrice, data: data))
     }
 
diff --git a/EthereumKit/Classes/Api/JsonRpc/EstimateGasJsonRpc.swift b/EthereumKit/Classes/Api/JsonRpc/EstimateGasJsonRpc.swift
index aa6c6979..281b1780 100644
--- a/EthereumKit/Classes/Api/JsonRpc/EstimateGasJsonRpc.swift
+++ b/EthereumKit/Classes/Api/JsonRpc/EstimateGasJsonRpc.swift
@@ -2,12 +2,14 @@ import BigInt
 
 class EstimateGasJsonRpc: IntJsonRpc {
 
-    init(from: Address, to: Address, amount: BigUInt?, gasLimit: Int?, gasPrice: Int?, data: Data?) {
+    init(from: Address, to: Address?, amount: BigUInt?, gasLimit: Int?, gasPrice: Int?, data: Data?) {
         var params: [String: Any] = [
-            "from": from.hex,
-            "to": to.hex
+            "from": from.hex
         ]
 
+        if let to = to {
+            params["to"] = to.hex
+        }
         if let amount = amount {
             params["value"] = "0x" + amount.serialize().hex.removeLeadingZeros()
         }
diff --git a/EthereumKit/Classes/Core/Kit.swift b/EthereumKit/Classes/Core/Kit.swift
index 7b071f5c..81ca3786 100644
--- a/EthereumKit/Classes/Core/Kit.swift
+++ b/EthereumKit/Classes/Core/Kit.swift
@@ -200,7 +200,7 @@ extension Kit {
         return blockchain.estimateGas(to: to, amount: resolvedAmount, gasLimit: maxGasLimit, gasPrice: gasPrice, data: nil)
     }
 
-    public func estimateGas(to: Address, amount: BigUInt?, gasPrice: Int?, data: Data?) -> Single<Int> {
+    public func estimateGas(to: Address?, amount: BigUInt?, gasPrice: Int?, data: Data?) -> Single<Int> {
         blockchain.estimateGas(to: to, amount: amount, gasLimit: maxGasLimit, gasPrice: gasPrice, data: data)
     }
 
diff --git a/EthereumKit/Classes/Core/Protocols.swift b/EthereumKit/Classes/Core/Protocols.swift
index 6eb0782d..b6cd4f20 100644
--- a/EthereumKit/Classes/Core/Protocols.swift
+++ b/EthereumKit/Classes/Core/Protocols.swift
@@ -21,7 +21,7 @@ protocol IBlockchain {
     func transactionSingle(transactionHash: Data) -> Single<RpcTransaction?>
     func getStorageAt(contractAddress: Address, positionData: Data, defaultBlockParameter: DefaultBlockParameter) -> Single<Data>
     func call(contractAddress: Address, data: Data, defaultBlockParameter: DefaultBlockParameter) -> Single<Data>
-    func estimateGas(to: Address, amount: BigUInt?, gasLimit: Int?, gasPrice: Int?, data: Data?) -> Single<Int>
+    func estimateGas(to: Address?, amount: BigUInt?, gasLimit: Int?, gasPrice: Int?, data: Data?) -> Single<Int>
 }
 
 protocol IBlockchainDelegate: class {
diff --git a/EthereumKit/Classes/Spv/Core/SpvBlockchain.swift b/EthereumKit/Classes/Spv/Core/SpvBlockchain.swift
index 84d8a030..53634803 100644
--- a/EthereumKit/Classes/Spv/Core/SpvBlockchain.swift
+++ b/EthereumKit/Classes/Spv/Core/SpvBlockchain.swift
@@ -110,7 +110,7 @@ extension SpvBlockchain: IBlockchain {
 //        rpcApiProvider.call(contractAddress: contractAddress, data: data, defaultBlockParameter: defaultBlockParameter)
     }
 
-    func estimateGas(to: Address, amount: BigUInt?, gasLimit: Int?, gasPrice: Int?, data: Data?) -> Single<Int> {
+    func estimateGas(to: Address?, amount: BigUInt?, gasLimit: Int?, gasPrice: Int?, data: Data?) -> Single<Int> {
         fatalError("Not implemented yet")
 //        rpcApiProvider.getEstimateGas(to: to, amount: amount, gasLimit: gasLimit, gasPrice: gasPrice, data: data)
     }