diff --git a/proof_iavl_absence.go b/proof_iavl_absence.go
index e08112e7e..51edd5a5d 100644
--- a/proof_iavl_absence.go
+++ b/proof_iavl_absence.go
@@ -15,7 +15,7 @@ const ProofOpIAVLAbsence = "iavl:a"
 // is good.
 type IAVLAbsenceOp struct {
 	// Encoded in ProofOp.Key.
-	key string
+	key []byte
 
 	// To encode in ProofOp.Data.
 	// Proof is nil for an empty tree.
@@ -25,7 +25,7 @@ type IAVLAbsenceOp struct {
 
 var _ merkle.ProofOperator = IAVLAbsenceOp{}
 
-func NewIAVLAbsenceOp(key string, proof *RangeProof) IAVLAbsenceOp {
+func NewIAVLAbsenceOp(key []byte, proof *RangeProof) IAVLAbsenceOp {
 	return IAVLAbsenceOp{
 		key:   key,
 		Proof: proof,
@@ -82,6 +82,6 @@ func (op IAVLAbsenceOp) Run(args [][]byte) ([][]byte, error) {
 	return [][]byte{root}, nil
 }
 
-func (op IAVLAbsenceOp) GetKey() string {
+func (op IAVLAbsenceOp) GetKey() []byte {
 	return op.key
 }
diff --git a/proof_iavl_value.go b/proof_iavl_value.go
index 7490a5b3f..a2cbf122d 100644
--- a/proof_iavl_value.go
+++ b/proof_iavl_value.go
@@ -16,7 +16,7 @@ const ProofOpIAVLValue = "iavl:v"
 // is good.
 type IAVLValueOp struct {
 	// Encoded in ProofOp.Key.
-	key string
+	key []byte
 
 	// To encode in ProofOp.Data.
 	// Proof is nil for an empty tree.
@@ -26,7 +26,7 @@ type IAVLValueOp struct {
 
 var _ merkle.ProofOperator = IAVLValueOp{}
 
-func NewIAVLValueOp(key string, proof *RangeProof) IAVLValueOp {
+func NewIAVLValueOp(key []byte, proof *RangeProof) IAVLValueOp {
 	return IAVLValueOp{
 		key:   key,
 		Proof: proof,
@@ -81,6 +81,6 @@ func (op IAVLValueOp) Run(args [][]byte) ([][]byte, error) {
 	return [][]byte{root}, nil
 }
 
-func (op IAVLValueOp) GetKey() string {
+func (op IAVLValueOp) GetKey() []byte {
 	return op.key
 }