diff --git a/src/actions/SendFormActions.js b/src/actions/SendFormActions.js
index f26664f3..ddd8ddf5 100644
--- a/src/actions/SendFormActions.js
+++ b/src/actions/SendFormActions.js
@@ -397,7 +397,7 @@ const estimateGasPrice = (): AsyncAction => async (dispatch: Dispatch, getState:
     }
 
     const requestedData = state.data;
-    const re = /^[0-9A-Fa-f]+$/g; // TODO: allow "0x" prefix
+    const re = /^(0x|0X)?[0-9A-Fa-f]+$/g;
     if (!re.test(requestedData)) {
         // stop "calculatingGasLimit" process
         dispatch(onGasLimitChange(requestedData.length > 0 ? state.gasLimit : network.defaultGasLimit.toString()));
diff --git a/src/actions/SendFormValidationActions.js b/src/actions/SendFormValidationActions.js
index 97c71ed4..4fb99bd4 100644
--- a/src/actions/SendFormValidationActions.js
+++ b/src/actions/SendFormValidationActions.js
@@ -19,7 +19,7 @@ const NUMBER_RE: RegExp = new RegExp('^(0|0\\.([0-9]+)?|[1-9][0-9]*\\.?([0-9]+)?
 const UPPERCASE_RE = new RegExp('^(.*[A-Z].*)$');
 const ABS_RE = new RegExp('^[0-9]+$');
 const ETH_18_RE = new RegExp('^(0|0\\.([0-9]{0,18})?|[1-9][0-9]*\\.?([0-9]{0,18})?|\\.[0-9]{0,18})$');
-const HEX_RE = new RegExp('^[0-9A-Fa-f]+$');
+const HEX_RE = new RegExp('^(0x|0X)?[0-9A-Fa-f]+$');
 const dynamicRegexp = (decimals: number): RegExp => {
     if (decimals > 0) {
         return new RegExp(`^(0|0\\.([0-9]{0,${decimals}})?|[1-9][0-9]*\\.?([0-9]{0,${decimals}})?|\\.[0-9]{1,${decimals}})$`);
diff --git a/src/actions/TxActions.js b/src/actions/TxActions.js
index 67c93c9f..ad34a5e7 100644
--- a/src/actions/TxActions.js
+++ b/src/actions/TxActions.js
@@ -5,6 +5,7 @@ import EthereumjsUnits from 'ethereumjs-units';
 import BigNumber from 'bignumber.js';
 import { toHex } from 'web3-utils'; // eslint-disable-line import/no-extraneous-dependencies
 import { initWeb3 } from 'actions/Web3Actions';
+import * as ethUtils from 'utils/ethUtils';
 
 import type {
     Dispatch,
@@ -29,10 +30,9 @@ type EthereumTxRequest = {
 export const prepareEthereumTx = (tx: EthereumTxRequest): PromiseAction<EthereumTransaction> => async (dispatch: Dispatch): Promise<EthereumTransaction> => {
     const instance = await dispatch(initWeb3(tx.network));
     const { token } = tx;
-    let data: string = `0x${tx.data}`; // TODO: check if already prefixed
+    let data: string = ethUtils.sanitizeHex(tx.data); // TODO: check if already prefixed
     let value: string = toHex(EthereumjsUnits.convert(tx.amount, 'ether', 'wei'));
     let to: string = tx.to; // eslint-disable-line prefer-destructuring
-
     if (token) {
         // smart contract transaction
         const contract = instance.erc20.clone();
diff --git a/src/actions/Web3Actions.js b/src/actions/Web3Actions.js
index 53c26a3b..2c3d9131 100644
--- a/src/actions/Web3Actions.js
+++ b/src/actions/Web3Actions.js
@@ -7,6 +7,7 @@ import EthereumjsUnits from 'ethereumjs-units';
 import type { EstimateGasOptions } from 'web3';
 import * as WEB3 from 'actions/constants/web3';
 import * as PENDING from 'actions/constants/pendingTx';
+import * as ethUtils from 'utils/ethUtils';
 
 import type {
     Dispatch,
@@ -272,8 +273,7 @@ export const updateGasPrice = (network: string): PromiseAction<void> => async (d
 
 export const estimateGasLimit = (network: string, $options: EstimateGasOptions): PromiseAction<string> => async (dispatch: Dispatch): Promise<string> => {
     const instance = await dispatch(initWeb3(network));
-    // TODO: allow data starting with 0x ...
-    const data = `0x${$options.data.length % 2 === 0 ? $options.data : `0${$options.data}`}`;
+    const data = ethUtils.sanitizeHex($options.data);
     const options = {
         ...$options,
         to: '0x0000000000000000000000000000000000000000',
diff --git a/src/utils/ethUtils.js b/src/utils/ethUtils.js
index 2d4b553e..94e61a6f 100644
--- a/src/utils/ethUtils.js
+++ b/src/utils/ethUtils.js
@@ -7,15 +7,14 @@ export const decimalToHex = (dec: number): string => new BigNumber(dec).toString
 
 export const padLeftEven = (hex: string): string => (hex.length % 2 !== 0 ? `0${hex}` : hex);
 
-export const sanitizeHex = ($hex: number | string): ?string => {
-    if (typeof $hex !== 'string') return null;
-    const hex = $hex.substring(0, 2) === '0x' ? $hex.substring(2) : $hex;
+export const sanitizeHex = ($hex: string): string => {
+    const hex = $hex.toLowerCase().substring(0, 2) === '0x' ? $hex.substring(2) : $hex;
     if (hex === '') return '';
     return `0x${padLeftEven(hex)}`;
 };
 
 export const hexToDecimal = (hex: number): string => {
-    const sanitized: ?string = sanitizeHex(hex);
+    const sanitized: ?string = sanitizeHex(hex.toString());
     return !sanitized ? 'null' : new BigNumber(sanitized).toString();
 };