diff --git a/contracts/common/BiconomyTokenPaymasterErrors.sol b/contracts/common/BiconomyTokenPaymasterErrors.sol
index 6188f11..845d87f 100644
--- a/contracts/common/BiconomyTokenPaymasterErrors.sol
+++ b/contracts/common/BiconomyTokenPaymasterErrors.sol
@@ -71,6 +71,11 @@ contract BiconomyTokenPaymasterErrors {
      */
     error InvalidOracleDecimals();
 
+    /**
+     * @notice Throws when price expiry duration is in the past
+     */
+    error InvalidPriceExpiryDuration();
+
     /**
      * @notice Throws when external signer's signature has invalid length
      */
diff --git a/contracts/token/BiconomyTokenPaymaster.sol b/contracts/token/BiconomyTokenPaymaster.sol
index 07ce080..ff2d048 100644
--- a/contracts/token/BiconomyTokenPaymaster.sol
+++ b/contracts/token/BiconomyTokenPaymaster.sol
@@ -104,7 +104,9 @@ contract BiconomyTokenPaymaster is
             // ETH -> USD will always have 8 decimals for Chainlink and TWAP
             revert InvalidOracleDecimals();
         }
-        require(block.timestamp >= priceExpiryDurationArg, "Price expiry duration cannot be in the past");
+        if (block.timestamp < priceExpiryDurationArg) {
+            revert InvalidPriceExpiryDuration();
+        }
 
         // Set state variables
         assembly ("memory-safe") {
@@ -271,7 +273,7 @@ contract BiconomyTokenPaymaster is
      * @notice only to be called by the owner of the contract.
      */
     function setPriceExpiryDuration(uint256 newPriceExpiryDuration) external payable onlyOwner {
-        require(block.timestamp >= newPriceExpiryDuration, "Price expiry duration cannot be in the past");
+        if(block.timestamp < newPriceExpiryDuration) revert InvalidPriceExpiryDuration();
         uint256 oldPriceExpiryDuration = priceExpiryDuration;
         assembly ("memory-safe") {
             sstore(priceExpiryDuration.slot, newPriceExpiryDuration)
@@ -515,7 +517,7 @@ contract BiconomyTokenPaymaster is
 
             // deduct max penalty from the token amount we pass to the postOp
             // so we don't refund it at postOp
-            context = abi.encode(userOp.sender, tokenAddress, tokenAmount-((maxPenalty*tokenPrice*externalPriceMarkup)/(1e18*_PRICE_DENOMINATOR)), tokenPrice, externalPriceMarkup, userOpHash);
+            context = abi.encode(userOp.sender, tokenAddress, tokenAmount-((maxPenalty*tokenPrice*externalPriceMarkup)/(_NATIVE_TOKEN_DECIMALS*_PRICE_DENOMINATOR)), tokenPrice, externalPriceMarkup, userOpHash);
             validationData = _packValidationData(false, validUntil, validAfter);
         } else if (mode == PaymasterMode.INDEPENDENT) {
             // Use only oracles for the token specified in modeSpecificData
@@ -543,7 +545,7 @@ contract BiconomyTokenPaymaster is
             SafeTransferLib.safeTransferFrom(tokenAddress, userOp.sender, address(this), tokenAmount);
 
             context =
-                abi.encode(userOp.sender, tokenAddress, tokenAmount-((maxPenalty*tokenPrice*independentPriceMarkup)/(1e18*_PRICE_DENOMINATOR)), tokenPrice, independentPriceMarkup, userOpHash);
+                abi.encode(userOp.sender, tokenAddress, tokenAmount-((maxPenalty*tokenPrice*independentPriceMarkup)/(_NATIVE_TOKEN_DECIMALS*_PRICE_DENOMINATOR)), tokenPrice, independentPriceMarkup, userOpHash);
             validationData = 0; // Validation success and price is valid indefinetly
         }
     }