diff --git a/packages/protocol/contracts/L1/LibData.sol b/packages/protocol/contracts/L1/LibData.sol
index d753a798a83..d7d7f884fcc 100644
--- a/packages/protocol/contracts/L1/LibData.sol
+++ b/packages/protocol/contracts/L1/LibData.sol
@@ -63,7 +63,9 @@ library LibData {
         // Changed when a block is proven/finalized
         uint64 latestVerifiedHeight;
         uint64 latestVerifiedId;
-        uint64 avgProofTime; // the proof time moving average
+        // the proof time moving average, note that for each block, only the
+        // first proof's time is considered.
+        uint64 avgProofTime;
         uint64 __reservedC1;
         // Reserved
         uint256[42] __gap;