diff --git a/rpc/v0/json_service_data_test.go b/rpc/v0/json_service_data_test.go
new file mode 100644
index 0000000000000000000000000000000000000000..e37f6733291b061e1eff915da304e0c03a70c6e9
--- /dev/null
+++ b/rpc/v0/json_service_data_test.go
@@ -0,0 +1,71 @@
+// Copyright 2017 Monax Industries Limited
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//  http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package rpc_v0
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/eris-ltd/eris-db/rpc"
+	"github.com/eris-ltd/eris-db/txs"
+
+	"github.com/stretchr/testify/assert"
+)
+
+var testBroadcastCallTxJsonRequest = []byte(`
+{
+  "id": "57EC1D39-7B3D-4F96-B286-8FC128177AFC4",
+  "jsonrpc": "2.0",
+  "method": "erisdb.broadcastTx",
+  "params": [
+    2,
+    {
+      "address": "5A9083BB0EFFE4C8EB2ADD29174994F73E77D418",
+      "data": "2F2397A00000000000000000000000000000000000000000000000000000000000003132",
+      "fee": 1,
+      "gas_limit": 1000000,
+      "input": {
+        "address": "BE18FDCBF12BF99F4D75325E17FF2E78F1A35FE8",
+        "amount": 1,
+        "pub_key": [
+          1,
+          "8D1611925948DC2EDDF739FB65CE517757D286155A039B28441C3349BE9A8C38"
+        ],
+        "sequence": 2,
+        "signature": [
+          1,
+          "B090D622F143ECEDA9B9E7B15485CE7504453C05434951CF867B013D80ED1BD2A0CA32846FC175D234CDFB9D5C3D792759E8FE79FD4DB3006B24950EE3C37D00"
+        ]
+      }
+    }
+  ]
+}`)
+
+// strictly test the codec for go-wire encoding of the Json format,
+// This should restore compatibility with the format on v0.11.4
+// (which was broken on v0.12)
+func TestCallTxJsonFormatCodec(t *testing.T) {
+	codec := NewTCodec()
+	param := new(txs.Tx)
+
+	// Create new request object and unmarshal.
+	request := &rpc.RPCRequest{}
+	assert.NoError(t, json.Unmarshal(testBroadcastCallTxJsonRequest, request),
+		"Provided JSON test data does not unmarshal to rpc.RPCRequest object.")
+	assert.NoError(t, codec.DecodeBytes(param, request.Params),
+		"RPC codec failed to decode params as transaction type.")
+	_, ok := (*param).(*txs.CallTx)
+	assert.True(t, ok, "Type byte 0x02 should unmarshal into CallTx.")
+}