diff --git a/signer/core/apitypes/types.go b/signer/core/apitypes/types.go
index 49819fee3..6bab4ce35 100644
--- a/signer/core/apitypes/types.go
+++ b/signer/core/apitypes/types.go
@@ -251,6 +251,25 @@ type TypedDataDomain struct {
 	Salt              string                `json:"salt"`
 }
 
+// TypedDataAndHash is a helper function that calculates a hash for typed data conforming to EIP-712.
+// This hash can then be safely used to calculate a signature.
+//
+// See https://eips.ethereum.org/EIPS/eip-712 for the full specification.
+//
+// This gives context to the signed typed data and prevents signing of transactions.
+func TypedDataAndHash(typedData TypedData) ([]byte, string, error) {
+	domainSeparator, err := typedData.HashStruct("EIP712Domain", typedData.Domain.Map())
+	if err != nil {
+		return nil, "", err
+	}
+	typedDataHash, err := typedData.HashStruct(typedData.PrimaryType, typedData.Message)
+	if err != nil {
+		return nil, "", err
+	}
+	rawData := fmt.Sprintf("\x19\x01%s%s", string(domainSeparator), string(typedDataHash))
+	return crypto.Keccak256([]byte(rawData)), rawData, nil
+}
+
 // HashStruct generates a keccak256 hash of the encoding of the provided data
 func (typedData *TypedData) HashStruct(primaryType string, data TypedDataMessage) (hexutil.Bytes, error) {
 	encodedData, err := typedData.EncodeData(primaryType, data, 1)
diff --git a/signer/core/signed_data.go b/signer/core/signed_data.go
index 1b4e91cb6..c0da22e62 100644
--- a/signer/core/signed_data.go
+++ b/signer/core/signed_data.go
@@ -233,23 +233,17 @@ func (api *SignerAPI) SignTypedData(ctx context.Context, addr common.MixedcaseAd
 // - the signature preimage (hash)
 func (api *SignerAPI) signTypedData(ctx context.Context, addr common.MixedcaseAddress,
 	typedData apitypes.TypedData, validationMessages *apitypes.ValidationMessages) (hexutil.Bytes, hexutil.Bytes, error) {
-	domainSeparator, err := typedData.HashStruct("EIP712Domain", typedData.Domain.Map())
+	sighash, rawData, err := apitypes.TypedDataAndHash(typedData)
 	if err != nil {
 		return nil, nil, err
 	}
-	typedDataHash, err := typedData.HashStruct(typedData.PrimaryType, typedData.Message)
-	if err != nil {
-		return nil, nil, err
-	}
-	rawData := []byte(fmt.Sprintf("\x19\x01%s%s", string(domainSeparator), string(typedDataHash)))
-	sighash := crypto.Keccak256(rawData)
 	messages, err := typedData.Format()
 	if err != nil {
 		return nil, nil, err
 	}
 	req := &SignDataRequest{
 		ContentType: apitypes.DataTyped.Mime,
-		Rawdata:     rawData,
+		Rawdata:     []byte(rawData),
 		Messages:    messages,
 		Hash:        sighash,
 		Address:     addr}