diff --git a/src/hash.ts b/src/hash.ts
index 2c2e32de..e9e40ca7 100644
--- a/src/hash.ts
+++ b/src/hash.ts
@@ -3,7 +3,7 @@ const createHash = require('create-hash')
 const ethjsUtil = require('ethjs-util')
 import * as rlp from 'rlp'
 import { toBuffer, setLengthLeft } from './bytes'
-import { assertIsString, assertIsBuffer, assertIsArray } from './helpers'
+import { assertIsString, assertIsBuffer, assertIsArray, assertIsHexString } from './helpers'
 
 /**
  * Creates Keccak hash of a Buffer input
@@ -26,23 +26,26 @@ export const keccak256 = function(a: Buffer): Buffer {
 }
 
 /**
- * Creates Keccak hash of a String input
- * @param a The input data (String) If string is 0x-prefixed hex value it's
- *          interpreted as hexadecimal, otherwise as utf8.
+ * Creates Keccak hash of a utf-8 string input
+ * @param a The input data (String)
  * @param bits (number = 256) The Keccak width
  */
 export const keccakFromString = function(a: string, bits: number = 256) {
   assertIsString(a)
-  let buf
-  if (!ethjsUtil.isHexString(a)) {
-    buf = Buffer.from(a, 'utf8')
-  } else {
-    buf = toBuffer(a)
-  }
-
+  const buf = Buffer.from(a, 'utf8')
   return keccak(buf, bits)
 }
 
+/**
+ * Creates Keccak hash of an 0x-prefixed string input
+ * @param a The input data (String)
+ * @param bits (number = 256) The Keccak width
+ */
+export const keccakFromHexString = function(a: string, bits: number = 256) {
+  assertIsHexString(a)
+  return keccak(toBuffer(a), bits)
+}
+
 /**
  * Creates Keccak hash of a number array input
  * @param a The input data (number[])
diff --git a/test/hash.spec.ts b/test/hash.spec.ts
index b7dad973..a76d0c90 100644
--- a/test/hash.spec.ts
+++ b/test/hash.spec.ts
@@ -3,6 +3,7 @@ import {
   keccak,
   keccak256,
   keccakFromString,
+  keccakFromHexString,
   keccakFromArray,
   sha256,
   sha256FromString,
@@ -39,13 +40,7 @@ describe('keccak256', function() {
 })
 
 describe('keccakFromString', function() {
-  it('with hexprefix should produce a hash', function() {
-    const msg = '0x3c9229289a6125f7fdf1885a77bb12c37a8d3b4962d936f7e3084dece32a3ca1'
-    const r = '82ff40c0a986c6a5cfad4ddf4c3aa6996f1a7837f9c398e17e5de5cbd5a12b28'
-    const hash = keccakFromString(msg)
-    assert.equal(hash.toString('hex'), r)
-  })
-  it('without hexprefix should produce a hash', function() {
+  it('should produce a hash', function() {
     const msg = '3c9229289a6125f7fdf1885a77bb12c37a8d3b4962d936f7e3084dece32a3ca1'
     const r = '22ae1937ff93ec72c4d46ff3e854661e3363440acd6f6e4adf8f1a8978382251'
     const hash = keccakFromString(msg)
@@ -59,6 +54,27 @@ describe('keccakFromString', function() {
   })
 })
 
+describe('keccakFromHexString', function() {
+  it('should produce a hash', function() {
+    const msg = '0x3c9229289a6125f7fdf1885a77bb12c37a8d3b4962d936f7e3084dece32a3ca1'
+    const r = '82ff40c0a986c6a5cfad4ddf4c3aa6996f1a7837f9c398e17e5de5cbd5a12b28'
+    const hash = keccakFromHexString(msg)
+    assert.equal(hash.toString('hex'), r)
+  })
+  it('should throw if input is not hex-prefixed', function() {
+    const msg = '3c9229289a6125f7fdf1885a77bb12c37a8d3b4962d936f7e3084dece32a3ca1'
+    assert.throws(function() {
+      keccakFromHexString(msg)
+    })
+  })
+  it('should throw if input is not a string', function() {
+    const buf = toBuffer('0x3c9229289a6125f7fdf1885a77bb12c37a8d3b4962d936f7e3084dece32a3ca1')
+    assert.throws(function() {
+      keccakFromHexString((<unknown>buf) as string)
+    })
+  })
+})
+
 describe('keccakFromArray', function() {
   it('should produce a hash', function() {
     const arr = [0, 1, 2, 3, 4, 5, 6, 7, 8, 0]