diff --git a/chain/types/ethtypes/eth_types.go b/chain/types/ethtypes/eth_types.go
index f157c7f94c5..02b0012be6e 100644
--- a/chain/types/ethtypes/eth_types.go
+++ b/chain/types/ethtypes/eth_types.go
@@ -548,12 +548,12 @@ func (h EthSubscriptionID) String() string {
 }
 
 type EthFilterSpec struct {
-	// Interpreted as an epoch or one of "latest" for last mined block, "earliest" for first,
+	// Interpreted as an epoch (in hex) or one of "latest" for last mined block, "earliest" for first,
 	// "pending" for not yet committed messages.
 	// Optional, default: "latest".
 	FromBlock *string `json:"fromBlock,omitempty"`
 
-	// Interpreted as an epoch or one of "latest" for last mined block, "earliest" for first,
+	// Interpreted as an epoch (in hex) or one of "latest" for last mined block, "earliest" for first,
 	// "pending" for not yet committed messages.
 	// Optional, default: "latest".
 	ToBlock *string `json:"toBlock,omitempty"`
diff --git a/node/impl/full/eth.go b/node/impl/full/eth.go
index e2c39ed878f..a3898a26661 100644
--- a/node/impl/full/eth.go
+++ b/node/impl/full/eth.go
@@ -9,6 +9,7 @@ import (
 	"os"
 	"sort"
 	"strconv"
+	"strings"
 	"sync"
 	"time"
 
@@ -1180,6 +1181,9 @@ func (e *EthEvent) installEthFilterSpec(ctx context.Context, filterSpec *ethtype
 		} else if *filterSpec.FromBlock == "pending" {
 			return nil, api.ErrNotSupported
 		} else {
+			if !strings.HasPrefix(*filterSpec.FromBlock, "0x") {
+				return nil, xerrors.Errorf("FromBlock is not a hex")
+			}
 			epoch, err := ethtypes.EthUint64FromHex(*filterSpec.FromBlock)
 			if err != nil {
 				return nil, xerrors.Errorf("invalid epoch")
@@ -1195,6 +1199,9 @@ func (e *EthEvent) installEthFilterSpec(ctx context.Context, filterSpec *ethtype
 		} else if *filterSpec.ToBlock == "pending" {
 			return nil, api.ErrNotSupported
 		} else {
+			if !strings.HasPrefix(*filterSpec.ToBlock, "0x") {
+				return nil, xerrors.Errorf("ToBlock is not a hex")
+			}
 			epoch, err := ethtypes.EthUint64FromHex(*filterSpec.ToBlock)
 			if err != nil {
 				return nil, xerrors.Errorf("invalid epoch")