diff --git a/backend/mpc-system/services/service-party-app/tss-party/main.go b/backend/mpc-system/services/service-party-app/tss-party/main.go
index 2d227420..dc897492 100644
--- a/backend/mpc-system/services/service-party-app/tss-party/main.go
+++ b/backend/mpc-system/services/service-party-app/tss-party/main.go
@@ -611,7 +611,10 @@ func executeSign(
 	// This is required when signing with a subset of the original keygen participants.
 	// BuildLocalSaveDataSubset filters the Ks, BigXj, NTildej, H1j, H2j, and PaillierPKs
 	// arrays to only include data for the participating signers.
+	fmt.Fprintf(os.Stderr, "[TSS-SIGN] Original keygenData has %d parties (Ks length)\n", len(keygenData.Ks))
+	fmt.Fprintf(os.Stderr, "[TSS-SIGN] Building subset for %d signing parties\n", len(sortedPartyIDs))
 	subsetKeygenData := keygen.BuildLocalSaveDataSubset(keygenData, sortedPartyIDs)
+	fmt.Fprintf(os.Stderr, "[TSS-SIGN] Subset keygenData has %d parties (Ks length)\n", len(subsetKeygenData.Ks))
 
 	// Create channels
 	outCh := make(chan tss.Message, thresholdT*10)