diff --git a/contracts/common/Errors.sol b/contracts/common/Errors.sol
index 35738f1..4e4fad2 100644
--- a/contracts/common/Errors.sol
+++ b/contracts/common/Errors.sol
@@ -20,6 +20,16 @@ contract SponsorshipPaymasterErrors {
      */
     error VerifyingSignerCannotBeZero();
 
+    /**
+     * @notice Throws when the paymaster id provided is a deployed contract   
+     */
+    error PaymasterIdCannotBeContract();
+
+    /**
+     * @notice Throws when the fee collector address provided is a deployed contract
+     */
+    error FeeCollectorCannotBeContract();
+
     /**
      * @notice Throws when the fee collector address provided is address(0)
      */
diff --git a/contracts/libs/AddressUtils.sol b/contracts/libs/AddressUtils.sol
new file mode 100644
index 0000000..43cb832
--- /dev/null
+++ b/contracts/libs/AddressUtils.sol
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.20;
+
+
+/**
+ * Utility library of inline functions on addresses
+ */
+library AddressUtils {
+
+  /**
+   * Returns whether the target address is a contract
+   * @dev This function will return false if invoked during the constructor of a contract,
+   * as the code is not actually created until after the constructor finishes.
+   * @param _addr address to check
+   * @return whether the target address is a contract
+   */
+  function isContract(address _addr) internal view returns (bool) {
+    uint256 size;
+    // XXX Currently there is no better way to check if there is a contract in an address
+    // than to check the size of the code at that address.
+    // See https://ethereum.stackexchange.com/a/14016/36603
+    // for more details about how this works.
+    // TODO Check this again before the Serenity release, because all addresses will be
+    // contracts then.
+    // solium-disable-next-line security/no-inline-assembly
+    assembly { size := extcodesize(_addr) }
+    return size > 0;
+  }
+
+}
\ No newline at end of file
diff --git a/contracts/sponsorship/SponsorshipPaymaster.sol b/contracts/sponsorship/SponsorshipPaymaster.sol
index c6a93bb..89b2c00 100644
--- a/contracts/sponsorship/SponsorshipPaymaster.sol
+++ b/contracts/sponsorship/SponsorshipPaymaster.sol
@@ -9,6 +9,7 @@ import {UserOperation, UserOperationLib} from "@account-abstraction/contracts/in
 import "../BasePaymaster.sol";
 import {SponsorshipPaymasterErrors} from "../common/Errors.sol";
 import {MathLib} from "../libs/MathLib.sol";
+import {AddressUtils} from "../libs/AddressUtils.sol";
 import {ISponsorshipPaymaster} from "../interfaces/paymasters/ISponsorshipPaymaster.sol";
 
 /**
@@ -29,6 +30,7 @@ contract SponsorshipPaymaster is
     ISponsorshipPaymaster
 {
     using ECDSA for bytes32;
+    using AddressUtils for address;
     using UserOperationLib for UserOperation;
 
     uint32 private constant PRICE_DENOMINATOR = 1e6;
@@ -72,11 +74,10 @@ contract SponsorshipPaymaster is
      * @param paymasterId dapp identifier for which deposit is being made
      */
     function depositFor(address paymasterId) external payable nonReentrant {
+        if(paymasterId.isContract()) revert PaymasterIdCannotBeContract();
         if (paymasterId == address(0)) revert PaymasterIdCannotBeZero();
         if (msg.value == 0) revert DepositCanNotBeZero();
-        paymasterIdBalances[paymasterId] =
-            paymasterIdBalances[paymasterId] +
-            msg.value;
+        paymasterIdBalances[paymasterId] += msg.value;
         entryPoint.depositTo{value: msg.value}(address(this));
         emit GasDeposited(paymasterId, msg.value);
     }
@@ -110,6 +111,7 @@ contract SponsorshipPaymaster is
     function setFeeCollector(
         address _newFeeCollector
     ) external payable onlyOwner {
+        if(_newFeeCollector.isContract()) revert FeeCollectorCannotBeContract();
         if (_newFeeCollector == address(0)) revert FeeCollectorCannotBeZero();
         address oldFeeCollector = feeCollector;
         assembly {
@@ -324,7 +326,6 @@ contract SponsorshipPaymaster is
         require(priceMarkup <= 2e6, "Verifying PM:high markup %");
 
         uint32 dynamicMarkup = MathLib.maxuint32(priceMarkup, fixedPriceMarkup);
-        require(dynamicMarkup >= 1e6, "Verifying PM:low markup %");
 
         uint256 effectiveCost = (requiredPreFund * dynamicMarkup) /
             PRICE_DENOMINATOR;