diff --git a/beacon_chain/attestation_pool.nim b/beacon_chain/attestation_pool.nim
index 02f2919e2..1c83c8299 100644
--- a/beacon_chain/attestation_pool.nim
+++ b/beacon_chain/attestation_pool.nim
@@ -1,6 +1,6 @@
 import
   deques, options, sequtils, tables,
-  chronicles, stew/bitseqs,
+  chronicles, stew/bitseqs, json_serialization/std/sets,
   ./spec/[beaconstate, datatypes, crypto, digest, helpers, validator],
   ./extras, ./beacon_chain_db, ./ssz, ./block_pool,
   beacon_node_types
diff --git a/beacon_chain/spec/state_transition_epoch.nim b/beacon_chain/spec/state_transition_epoch.nim
index 6d822c62e..058ca9cb9 100644
--- a/beacon_chain/spec/state_transition_epoch.nim
+++ b/beacon_chain/spec/state_transition_epoch.nim
@@ -226,7 +226,7 @@ proc process_justification_and_finalization(
   ## and
   ## https://github.com/ethereum/eth2.0-specs/blob/v0.8.2/specs/core/0_beacon-chain.md#final-updates
   ## after which the state.previous_epoch_attestations is replaced.
-  debug "Non-attesting indices in previous epoch: ",
+  trace "Non-attesting indices in previous epoch",
     missing_all_validators=
       difference(active_validator_indices,
         toSet(mapIt(get_attesting_indices(state,