diff --git a/contracts/sfc/NodeInterface.sol b/contracts/sfc/NodeInterface.sol
index b81940e..90ee06c 100644
--- a/contracts/sfc/NodeInterface.sol
+++ b/contracts/sfc/NodeInterface.sol
@@ -1,6 +1,6 @@
 pragma solidity ^0.5.0;
 
-contract NodeInterface {
+interface NodeInterface {
 
     event IncBalance(address indexed acc, uint256 value);
 //    event SetBalance(address indexed acc, uint256 value);
diff --git a/contracts/sfc/SFC.sol b/contracts/sfc/SFC.sol
index 8974281..c3b793c 100644
--- a/contracts/sfc/SFC.sol
+++ b/contracts/sfc/SFC.sol
@@ -1,6 +1,6 @@
 pragma solidity ^0.5.0;
 
-import "../common/SafeMath.sol";
+import "@openzeppelin/contracts/math/SafeMath.sol";
 import "./StakerConstants.sol";
 import "../ownership/Ownable.sol";
 import "../version/Version.sol";
diff --git a/contracts/sfc/StakerConstants.sol b/contracts/sfc/StakerConstants.sol
index 2c7aece..b88e04f 100644
--- a/contracts/sfc/StakerConstants.sol
+++ b/contracts/sfc/StakerConstants.sol
@@ -1,6 +1,6 @@
 pragma solidity ^0.5.0;
 
-import "../common/SafeMath.sol";
+import "@openzeppelin/contracts/math/SafeMath.sol";
 import "../common/Decimal.sol";
 
 contract StakersConstants {