diff --git a/sei-cosmos/storev2/rootmulti/store.go b/sei-cosmos/storev2/rootmulti/store.go
index baa0c14efc..1ead10c963 100644
--- a/sei-cosmos/storev2/rootmulti/store.go
+++ b/sei-cosmos/storev2/rootmulti/store.go
@@ -638,6 +638,19 @@ func (rs *Store) Query(req abci.RequestQuery) abci.ResponseQuery {
 
 	res := store.Query(req)
 
+	// When serving from a historical read-only memiavl instance, the response
+	// byte slices (Key, Value) may point directly into mmap'd memory that will
+	// be unmapped when the deferred scStore.Close() runs. Copy them so the
+	// caller doesn't hit a use-after-free segfault during JSON marshaling.
+	if !latest {
+		if len(res.Key) > 0 {
+			res.Key = append([]byte{}, res.Key...)
+		}
+		if len(res.Value) > 0 {
+			res.Value = append([]byte{}, res.Value...)
+		}
+	}
+
 	// If underlying query failed (e.g. invalid height/path) or doesn' need proof, return as-is.
 	if res.Code != 0 || !needProof {
 		return res
diff --git a/sei-tendermint/types/block.go b/sei-tendermint/types/block.go
index 21acdea1de..a918ed7c43 100644
--- a/sei-tendermint/types/block.go
+++ b/sei-tendermint/types/block.go
@@ -89,7 +89,9 @@ func (b *Block) ValidateBasic() error {
 	}
 
 	if w, g := b.LastCommit.Hash(), b.LastCommitHash; !bytes.Equal(w, g) {
-		return fmt.Errorf("wrong Header.LastCommitHash. Expected %X, got %X", w, g)
+		if wLegacy := b.LastCommit.LegacyHash(); !bytes.Equal(wLegacy, g) {
+			return fmt.Errorf("wrong Header.LastCommitHash. Expected %X, got %X", w, g)
+		}
 	}
 
 	// NOTE: b.Data.Txs may be nil, but b.Data.Hash() still works fine.
@@ -902,6 +904,25 @@ func (commit *Commit) Hash() tmbytes.HexBytes {
 	return commit.hash
 }
 
+// LegacyHash computes the commit hash using the pre-v6.4 algorithm, which
+// only includes signatures (not Height, Round, or BlockID). This is needed
+// to validate blocks that were created before the CommitHash change.
+func (commit *Commit) LegacyHash() tmbytes.HexBytes {
+	if commit == nil {
+		return nil
+	}
+	bs := make([][]byte, len(commit.Signatures))
+	for i, commitSig := range commit.Signatures {
+		pbcs := commitSig.ToProto()
+		bz, err := pbcs.Marshal()
+		if err != nil {
+			panic(err)
+		}
+		bs[i] = bz
+	}
+	return merkle.HashFromByteSlices(bs)
+}
+
 // StringIndented returns a string representation of the commit.
 func (commit *Commit) StringIndented(indent string) string {
 	if commit == nil {