diff --git a/contracts/tokenization/StableDebtToken.sol b/contracts/tokenization/StableDebtToken.sol
index 7663183e..328ea7f2 100644
--- a/contracts/tokenization/StableDebtToken.sol
+++ b/contracts/tokenization/StableDebtToken.sol
@@ -143,7 +143,7 @@ contract StableDebtToken is IStableDebtToken, DebtTokenBase {
     address _user,
     uint256 _amount,
     uint256 _rate
-  ) public override onlyLendingPool {
+  ) external override onlyLendingPool {
     MintLocalVars memory vars;
 
     //cumulates the user debt
@@ -193,7 +193,7 @@ contract StableDebtToken is IStableDebtToken, DebtTokenBase {
    * @param _user the address of the user
    * @param _amount the amount of debt tokens to mint
    **/
-  function burn(address _user, uint256 _amount) public override onlyLendingPool {
+  function burn(address _user, uint256 _amount) external override onlyLendingPool {
     (
       uint256 previousBalance,
       uint256 currentBalance,
diff --git a/contracts/tokenization/base/DebtTokenBase.sol b/contracts/tokenization/base/DebtTokenBase.sol
index 63412174..82c2479b 100644
--- a/contracts/tokenization/base/DebtTokenBase.sol
+++ b/contracts/tokenization/base/DebtTokenBase.sol
@@ -103,12 +103,12 @@ abstract contract DebtTokenBase is IERC20, VersionedInitializable {
    * @dev being non transferrable, the debt token does not implement any of the
    * standard ERC20 functions for transfer and allowance.
    **/
-  function transfer(address recipient, uint256 _amount) public virtual override returns (bool) {
+  function transfer(address recipient, uint256 _amount) external virtual override returns (bool) {
     revert('TRANSFER_NOT_SUPPORTED');
   }
 
   function allowance(address owner, address spender)
-    public
+    external
     virtual
     override
     view
@@ -117,7 +117,7 @@ abstract contract DebtTokenBase is IERC20, VersionedInitializable {
     revert('ALLOWANCE_NOT_SUPPORTED');
   }
 
-  function approve(address spender, uint256 _amount) public virtual override returns (bool) {
+  function approve(address spender, uint256 _amount) external virtual override returns (bool) {
     revert('APPROVAL_NOT_SUPPORTED');
   }
 
@@ -125,16 +125,16 @@ abstract contract DebtTokenBase is IERC20, VersionedInitializable {
     address sender,
     address recipient,
     uint256 _amount
-  ) public virtual override returns (bool) {
+  ) external virtual override returns (bool) {
     revert('TRANSFER_NOT_SUPPORTED');
   }
 
-  function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
+  function increaseAllowance(address spender, uint256 addedValue) external virtual returns (bool) {
     revert('ALLOWANCE_NOT_SUPPORTED');
   }
 
   function decreaseAllowance(address spender, uint256 subtractedValue)
-    public
+    external
     virtual
     returns (bool)
   {