diff --git a/rpc/args.go b/rpc/args.go
index d3449928b..b23216c98 100644
--- a/rpc/args.go
+++ b/rpc/args.go
@@ -388,8 +388,12 @@ func (args *Sha3Args) UnmarshalJSON(b []byte) (err error) {
 	if len(obj) < 1 {
 		return NewInsufficientParamsError(len(obj), 1)
 	}
-	args.Data = obj[0].(string)
 
+	argstr, ok := obj[0].(string)
+	if !ok {
+		return NewInvalidTypeError("data", "is not a string")
+	}
+	args.Data = argstr
 	return nil
 }
 
diff --git a/rpc/args_test.go b/rpc/args_test.go
index fa46f6515..0c7360c53 100644
--- a/rpc/args_test.go
+++ b/rpc/args_test.go
@@ -10,18 +10,6 @@ import (
 	"github.com/ethereum/go-ethereum/common"
 )
 
-func TestSha3(t *testing.T) {
-	input := `["0x68656c6c6f20776f726c64"]`
-	expected := "0x68656c6c6f20776f726c64"
-
-	args := new(Sha3Args)
-	json.Unmarshal([]byte(input), &args)
-
-	if args.Data != expected {
-		t.Error("got %s expected %s", input, expected)
-	}
-}
-
 func ExpectValidationError(err error) string {
 	var str string
 	switch err.(type) {
@@ -74,6 +62,47 @@ func ExpectDecodeParamError(err error) string {
 	return str
 }
 
+func TestSha3(t *testing.T) {
+	input := `["0x68656c6c6f20776f726c64"]`
+	expected := "0x68656c6c6f20776f726c64"
+
+	args := new(Sha3Args)
+	json.Unmarshal([]byte(input), &args)
+
+	if args.Data != expected {
+		t.Error("got %s expected %s", input, expected)
+	}
+}
+
+func TestSha3ArgsInvalid(t *testing.T) {
+	input := `{}`
+
+	args := new(Sha3Args)
+	str := ExpectDecodeParamError(json.Unmarshal([]byte(input), &args))
+	if len(str) > 0 {
+		t.Error(str)
+	}
+}
+
+func TestSha3ArgsEmpty(t *testing.T) {
+	input := `[]`
+
+	args := new(Sha3Args)
+	str := ExpectInsufficientParamsError(json.Unmarshal([]byte(input), &args))
+	if len(str) > 0 {
+		t.Error(str)
+	}
+}
+func TestSha3ArgsDataInvalid(t *testing.T) {
+	input := `[4]`
+
+	args := new(Sha3Args)
+	str := ExpectInvalidTypeError(json.Unmarshal([]byte(input), &args))
+	if len(str) > 0 {
+		t.Error(str)
+	}
+}
+
 func TestGetBalanceArgs(t *testing.T) {
 	input := `["0x407d73d8a49eeb85d32cf465507dd71d507100c1", "0x1f"]`
 	expected := new(GetBalanceArgs)
@@ -119,6 +148,8 @@ func TestGetBalanceArgsEmpty(t *testing.T) {
 
 	args := new(GetBalanceArgs)
 	str := ExpectInsufficientParamsError(json.Unmarshal([]byte(input), &args))
+	if len(str) > 0 {
+		t.Error(str)
 	}
 }