diff --git a/rpc/class.go b/rpc/class.go
index c51a942500..fd1bf2c1f9 100644
--- a/rpc/class.go
+++ b/rpc/class.go
@@ -56,8 +56,14 @@ func adaptDeclaredClass(declaredClass json.RawMessage) (core.Class, error) {
 		}
 		return sn2core.AdaptCairo1Class(feederClass.V1, compiledClass)
 	case feederClass.V0 != nil:
+		program := feederClass.V0.Program
+
 		// strip the quotes
-		base64Program := string(feederClass.V0.Program[1 : len(feederClass.V0.Program)-1])
+		if len(program) < 2 {
+			return nil, errors.New("invalid program")
+		}
+		base64Program := string(program[1 : len(program)-1])
+
 		feederClass.V0.Program, err = utils.Gzip64Decode(base64Program)
 		if err != nil {
 			return nil, err
diff --git a/rpc/estimate_fee_test.go b/rpc/estimate_fee_test.go
index fdc3699a8e..131a702600 100644
--- a/rpc/estimate_fee_test.go
+++ b/rpc/estimate_fee_test.go
@@ -14,6 +14,7 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"go.uber.org/mock/gomock"
+	"github.com/NethermindEth/juno/jsonrpc"
 )
 
 func TestEstimateFee(t *testing.T) {
@@ -65,6 +66,32 @@ func TestEstimateFee(t *testing.T) {
 		}), err)
 		require.Equal(t, httpHeader.Get(rpc.ExecutionStepsHeader), "0")
 	})
+
+	t.Run("transaction with invalid contract class", func(t *testing.T) {
+		toFelt := func(hex string) *felt.Felt {
+			return utils.HexToFelt(t, hex)
+		}
+		invalidTx := rpc.BroadcastedTransaction{
+			Transaction: rpc.Transaction{
+				Type:          rpc.TxnDeclare,
+				Version:       toFelt("0x1"),
+				Nonce:         toFelt("0x0"),
+				MaxFee:        toFelt("0x1"),
+				SenderAddress: toFelt("0x2"),
+				Signature: &[]*felt.Felt{
+					toFelt("0x123"),
+				},
+			},
+			ContractClass: json.RawMessage(`{}`),
+		}
+		_, _, err := handler.EstimateFee([]rpc.BroadcastedTransaction{invalidTx}, []rpc.SimulationFlag{}, rpc.BlockID{Latest: true})
+		expectedErr := &jsonrpc.Error{
+			Code:    jsonrpc.InvalidParams,
+			Message: "Invalid Params",
+			Data:    "invalid program",
+		}
+		require.Equal(t, expectedErr, err)
+	})
 }
 
 func assertEqualCairo0Class(t *testing.T, cairo0Class *core.Cairo0Class, class *rpc.Class) {