diff --git a/contracts/dnssec-oracle/BytesUtils.sol b/contracts/dnssec-oracle/BytesUtils.sol
index 96344ce5..a5bc4225 100644
--- a/contracts/dnssec-oracle/BytesUtils.sol
+++ b/contracts/dnssec-oracle/BytesUtils.sol
@@ -1,3 +1,4 @@
+//SPDX-License-Identifier: MIT
 pragma solidity ^0.8.4;
 
 library BytesUtils {
diff --git a/contracts/dnssec-oracle/RRUtils.sol b/contracts/dnssec-oracle/RRUtils.sol
index 20fbf15f..d44a6d4e 100644
--- a/contracts/dnssec-oracle/RRUtils.sol
+++ b/contracts/dnssec-oracle/RRUtils.sol
@@ -1,3 +1,4 @@
+//SPDX-License-Identifier: MIT
 pragma solidity ^0.8.4;
 
 import "./BytesUtils.sol";
diff --git a/contracts/registry/ENS.sol b/contracts/registry/ENS.sol
index d35f68e4..6b5a21dc 100644
--- a/contracts/registry/ENS.sol
+++ b/contracts/registry/ENS.sol
@@ -1,3 +1,4 @@
+//SPDX-License-Identifier: MIT
 pragma solidity >=0.8.4;
 
 interface ENS {
diff --git a/contracts/resolvers/OwnedResolver.sol b/contracts/resolvers/OwnedResolver.sol
index 5a6b581e..429f3b53 100644
--- a/contracts/resolvers/OwnedResolver.sol
+++ b/contracts/resolvers/OwnedResolver.sol
@@ -1,3 +1,4 @@
+//SPDX-License-Identifier: MIT
 pragma solidity >=0.8.4;
 import "@openzeppelin/contracts/access/Ownable.sol";
 import "./profiles/ABIResolver.sol";