diff --git a/rpc/args.go b/rpc/args.go
index 50b0f5826..65f0f6043 100644
--- a/rpc/args.go
+++ b/rpc/args.go
@@ -172,13 +172,8 @@ type NewSigArgs struct {
 }
 
 func (args *NewSigArgs) UnmarshalJSON(b []byte) (err error) {
-	var obj []json.RawMessage
-	var ext struct {
-		From string
-		Data string
-	}
+	var obj []interface{}
 
-	// Decode byte slice to array of RawMessages
 	if err := json.Unmarshal(b, &obj); err != nil {
 		return NewDecodeParamError(err.Error())
 	}
@@ -188,21 +183,26 @@ func (args *NewSigArgs) UnmarshalJSON(b []byte) (err error) {
 		return NewInsufficientParamsError(len(obj), 1)
 	}
 
-	// Decode 0th RawMessage to temporary struct
-	if err := json.Unmarshal(obj[0], &ext); err != nil {
-		return NewDecodeParamError(err.Error())
+	from, ok := obj[0].(string)
+	if !ok {
+		return NewInvalidTypeError("from", "not a string")
 	}
+	args.From = from
 
-	if len(ext.From) == 0 {
+	if len(args.From) == 0 {
 		return NewValidationError("from", "is required")
 	}
 
-	if len(ext.Data) == 0 {
+	data, ok := obj[1].(string)
+	if !ok {
+		return NewInvalidTypeError("data", "not a string")
+	}
+	args.Data = data
+
+	if len(args.Data) == 0 {
 		return NewValidationError("data", "is required")
 	}
 
-	args.From = ext.From
-	args.Data = ext.Data
 	return nil
 }
 
diff --git a/rpc/args_test.go b/rpc/args_test.go
index aef459961..fc10d68cf 100644
--- a/rpc/args_test.go
+++ b/rpc/args_test.go
@@ -2508,3 +2508,64 @@ func TestSourceArgsEmpty(t *testing.T) {
 		t.Error(str)
 	}
 }
+
+func TestSigArgs(t *testing.T) {
+	input := `["0xa94f5374fce5edbc8e2a8697c15331677e6ebf0b", "0x0"]`
+	expected := new(NewSigArgs)
+	expected.From = "0xa94f5374fce5edbc8e2a8697c15331677e6ebf0b"
+	expected.Data = "0x0"
+
+	args := new(NewSigArgs)
+	if err := json.Unmarshal([]byte(input), &args); err != nil {
+		t.Error(err)
+	}
+}
+
+func TestSigArgsEmptyData(t *testing.T) {
+	input := `["0xa94f5374fce5edbc8e2a8697c15331677e6ebf0b", ""]`
+
+	args := new(NewSigArgs)
+	str := ExpectValidationError(json.Unmarshal([]byte(input), args))
+	if len(str) > 0 {
+		t.Error(str)
+	}
+}
+
+func TestSigArgsDataType(t *testing.T) {
+	input := `["0xa94f5374fce5edbc8e2a8697c15331677e6ebf0b", 13]`
+
+	args := new(NewSigArgs)
+	str := ExpectInvalidTypeError(json.Unmarshal([]byte(input), args))
+	if len(str) > 0 {
+		t.Error(str)
+	}
+}
+
+func TestSigArgsEmptyFrom(t *testing.T) {
+	input := `["", "0x0"]`
+
+	args := new(NewSigArgs)
+	str := ExpectValidationError(json.Unmarshal([]byte(input), args))
+	if len(str) > 0 {
+		t.Error(str)
+	}
+}
+
+func TestSigArgsFromType(t *testing.T) {
+	input := `[false, "0x0"]`
+
+	args := new(NewSigArgs)
+	str := ExpectInvalidTypeError(json.Unmarshal([]byte(input), args))
+	if len(str) > 0 {
+		t.Error(str)
+	}
+}
+
+func TestSigArgsEmpty(t *testing.T) {
+	input := `[]`
+	args := new(NewSigArgs)
+	str := ExpectInsufficientParamsError(json.Unmarshal([]byte(input), args))
+	if len(str) > 0 {
+		t.Error(str)
+	}
+}