diff --git a/fvm/src/kernel/default.rs b/fvm/src/kernel/default.rs
index 3b4da07b9..13b69f98e 100644
--- a/fvm/src/kernel/default.rs
+++ b/fvm/src/kernel/default.rs
@@ -12,12 +12,14 @@ use fvm_ipld_blockstore::Blockstore;
 use fvm_ipld_encoding::{bytes_32, IPLD_RAW};
 use fvm_shared::address::Payload;
 use fvm_shared::bigint::Zero;
+use fvm_shared::chainid::ChainID;
 use fvm_shared::consensus::ConsensusFault;
 use fvm_shared::crypto::signature;
 use fvm_shared::econ::TokenAmount;
 use fvm_shared::error::ErrorNumber;
 use fvm_shared::event::ActorEvent;
 use fvm_shared::piece::{zero_piece_commitment, PaddedPieceSize};
+use fvm_shared::sector::RegisteredPoStProof::{StackedDRGWindow32GiBV1, StackedDRGWindow32GiBV1P1};
 use fvm_shared::sector::{RegisteredPoStProof, SectorInfo};
 use fvm_shared::sys::out::vm::ContextFlags;
 use fvm_shared::{commcid, ActorID};
@@ -539,9 +541,26 @@ where
             .call_manager
             .charge_gas(self.call_manager.price_list().on_verify_post(verify_info))?;
 
+        // Due to a bug on calibrationnet, we have some _valid_ StackedDRGWindow32GiBV1P1
+        // proofs that were deemed invalid on chain. This was fixed WITHOUT a network version check.
+        // As a result, we need to explicitly consider all such proofs invalid, ONLY on calibrationnet,
+        // and ONLY before epoch 498691,
+        let calibnet_chain_id = ChainID::from(314159);
+        let mut verify_info = verify_info.clone();
+
+        #[allow(clippy::collapsible_if)]
+        if self.call_manager.context().network.chain_id == calibnet_chain_id {
+            if self.call_manager.context().epoch <= 498691
+                && !verify_info.proofs.is_empty()
+                && verify_info.proofs[0].post_proof == StackedDRGWindow32GiBV1P1
+            {
+                verify_info.proofs[0].post_proof = StackedDRGWindow32GiBV1;
+            }
+        }
+
         // This is especially important to catch as, otherwise, a bad "post" could be undisputable.
         t.record(catch_and_log_panic("verifying post", || {
-            verify_post(verify_info)
+            verify_post(&verify_info)
         }))
     }