diff --git a/ui/app/components/app/modals/edit-approval-permission/edit-approval-permission.component.js b/ui/app/components/app/modals/edit-approval-permission/edit-approval-permission.component.js
index 53ff473e4..28f9fb1f9 100644
--- a/ui/app/components/app/modals/edit-approval-permission/edit-approval-permission.component.js
+++ b/ui/app/components/app/modals/edit-approval-permission/edit-approval-permission.component.js
@@ -4,6 +4,7 @@ import Modal from '../../modal'
 import Identicon from '../../../ui/identicon'
 import TextField from '../../../ui/text-field'
 import classnames from 'classnames'
+import BigNumber from 'bignumber.js'
 
 export default class EditApprovalPermission extends PureComponent {
   static propTypes = {
@@ -61,7 +62,7 @@ export default class EditApprovalPermission extends PureComponent {
             <div>{ t('balance') }</div>
           </div>
           <div className="edit-approval-permission__account-info__balance">
-            {`${tokenBalance} ${tokenSymbol}`}
+            {`${Number(tokenBalance).toPrecision(9)} ${tokenSymbol}`}
           </div>
         </div>
         <div className="edit-approval-permission__edit-section">
@@ -89,7 +90,7 @@ export default class EditApprovalPermission extends PureComponent {
                 'edit-approval-permission__edit-section__option-label--selected': selectedOptionIsUnlimited,
               })}>
                 {
-                  tokenAmount < tokenBalance
+                  (new BigNumber(tokenAmount)).lessThan(new BigNumber(tokenBalance))
                     ? t('proposedApprovalLimit')
                     : t('unlimited')
                 }
@@ -98,7 +99,7 @@ export default class EditApprovalPermission extends PureComponent {
                 { t('spendLimitRequestedBy', [origin]) }
               </div>
               <div className="edit-approval-permission__edit-section__option-value" >
-                {`${tokenAmount} ${tokenSymbol}`}
+                {`${Number(tokenAmount)} ${tokenSymbol}`}
               </div>
             </div>
           </div>
@@ -128,7 +129,7 @@ export default class EditApprovalPermission extends PureComponent {
                 <TextField
                   type="number"
                   min="0"
-                  placeholder={ `${customTokenAmount || tokenAmount} ${tokenSymbol}` }
+                  placeholder={ `${Number(customTokenAmount || tokenAmount)} ${tokenSymbol}` }
                   onChange={(event) => {
                     this.setState({ customSpendLimit: event.target.value })
                     if (selectedOptionIsUnlimited) {
diff --git a/ui/app/pages/confirm-approve/confirm-approve-content/confirm-approve-content.component.js b/ui/app/pages/confirm-approve/confirm-approve-content/confirm-approve-content.component.js
index 38644541d..d1acc6681 100644
--- a/ui/app/pages/confirm-approve/confirm-approve-content/confirm-approve-content.component.js
+++ b/ui/app/pages/confirm-approve/confirm-approve-content/confirm-approve-content.component.js
@@ -100,7 +100,7 @@ export default class ConfirmApproveContent extends Component {
         <div className="confirm-approve-content__small-text">{ t('accessAndSpendNotice', [origin]) }</div>
         <div className="flex-row">
           <div className="confirm-approve-content__label">{ t('amountWithColon') }</div>
-          <div className="confirm-approve-content__medium-text">{ `${customTokenAmount || tokenAmount} ${tokenSymbol}` }</div>
+          <div className="confirm-approve-content__medium-text">{ `${Number(customTokenAmount || tokenAmount)} ${tokenSymbol}` }</div>
         </div>
         <div className="flex-row">
           <div className="confirm-approve-content__label">{ t('toWithColon') }</div>
diff --git a/ui/app/pages/confirm-approve/confirm-approve.component.js b/ui/app/pages/confirm-approve/confirm-approve.component.js
index 3408a6ab8..2e02f6ba3 100644
--- a/ui/app/pages/confirm-approve/confirm-approve.component.js
+++ b/ui/app/pages/confirm-approve/confirm-approve.component.js
@@ -15,7 +15,7 @@ export default class ConfirmApprove extends Component {
   static propTypes = {
     tokenAddress: PropTypes.string,
     toAddress: PropTypes.string,
-    tokenAmount: PropTypes.number,
+    tokenAmount: PropTypes.string,
     tokenSymbol: PropTypes.string,
     fiatTransactionTotal: PropTypes.string,
     ethTransactionTotal: PropTypes.string,
@@ -33,7 +33,7 @@ export default class ConfirmApprove extends Component {
   }
 
   static defaultProps = {
-    tokenAmount: 0,
+    tokenAmount: '0',
   }
 
   state = {
@@ -69,14 +69,14 @@ export default class ConfirmApprove extends Component {
     } = this.props
     const { customPermissionAmount } = this.state
 
-    const tokensText = `${tokenAmount} ${tokenSymbol}`
+    const tokensText = `${Number(tokenAmount)} ${tokenSymbol}`
 
     const tokenBalance = tokenTrackerBalance
-      ? Number(calcTokenAmount(tokenTrackerBalance, decimals)).toPrecision(9)
+      ? calcTokenAmount(tokenTrackerBalance, decimals).toString(10)
       : ''
 
     const customData = customPermissionAmount
-      ? getCustomTxParamsData(data, { customPermissionAmount, tokenAmount, decimals })
+      ? getCustomTxParamsData(data, { customPermissionAmount, decimals })
       : null
 
     return (
@@ -92,7 +92,7 @@ export default class ConfirmApprove extends Component {
             this.setState({ customPermissionAmount: newAmount })
           }}
           customTokenAmount={String(customPermissionAmount)}
-          tokenAmount={String(tokenAmount)}
+          tokenAmount={tokenAmount}
           origin={origin}
           tokenSymbol={tokenSymbol}
           tokenBalance={tokenBalance}
diff --git a/ui/app/pages/confirm-approve/confirm-approve.container.js b/ui/app/pages/confirm-approve/confirm-approve.container.js
index 43f5aab90..5a3223564 100644
--- a/ui/app/pages/confirm-approve/confirm-approve.container.js
+++ b/ui/app/pages/confirm-approve/confirm-approve.container.js
@@ -43,7 +43,7 @@ const mapStateToProps = (state, ownProps) => {
   const tokenData = getTokenData(data)
   const tokenValue = tokenData && getTokenValue(tokenData.params)
   const toAddress = tokenData && getTokenToAddress(tokenData.params)
-  const tokenAmount = tokenData && calcTokenAmount(tokenValue, decimals).toNumber()
+  const tokenAmount = tokenData && calcTokenAmount(tokenValue, decimals).toString(10)
   const contractExchangeRate = contractExchangeRateSelector(state)
 
   const { origin } = transaction
diff --git a/ui/app/pages/confirm-approve/confirm-approve.util.js b/ui/app/pages/confirm-approve/confirm-approve.util.js
index be77c65f9..0318c6bed 100644
--- a/ui/app/pages/confirm-approve/confirm-approve.util.js
+++ b/ui/app/pages/confirm-approve/confirm-approve.util.js
@@ -1,28 +1,33 @@
 import { decimalToHex } from '../../helpers/utils/conversions.util'
 import { calcTokenValue } from '../../helpers/utils/token-util.js'
+import { getTokenData } from '../../helpers/utils/transactions.util'
 
-export function getCustomTxParamsData (data, { customPermissionAmount, tokenAmount, decimals }) {
-  if (customPermissionAmount) {
-    const tokenValue = decimalToHex(calcTokenValue(tokenAmount, decimals))
+export function getCustomTxParamsData (data, { customPermissionAmount, decimals }) {
+  const tokenData = getTokenData(data)
 
-    const re = new RegExp('(^.+)' + tokenValue + '$')
-    const matches = re.exec(data)
-
-    if (!matches || !matches[1]) {
-      return data
-    }
-    let dataWithoutCurrentAmount = matches[1]
-    const customPermissionValue = decimalToHex(calcTokenValue(Number(customPermissionAmount), decimals))
-
-    const differenceInLengths = customPermissionValue.length - tokenValue.length
-    const zeroModifier = dataWithoutCurrentAmount.length - differenceInLengths
-    if (differenceInLengths > 0) {
-      dataWithoutCurrentAmount = dataWithoutCurrentAmount.slice(0, zeroModifier)
-    } else if (differenceInLengths < 0) {
-      dataWithoutCurrentAmount = dataWithoutCurrentAmount.padEnd(zeroModifier, 0)
-    }
-
-    const customTxParamsData = dataWithoutCurrentAmount + customPermissionValue
-    return customTxParamsData
+  if (!tokenData) {
+    throw new Error('Invalid data')
+  } else if (tokenData.name !== 'approve') {
+    throw new Error(`Invalid data; should be 'approve' method, but instead is '${tokenData.name}'`)
   }
+  let spender = tokenData.params[0].value
+  if (spender.startsWith('0x')) {
+    spender = spender.substring(2)
+  }
+  const [signature, tokenValue] = data.split(spender)
+
+  if (!signature || !tokenValue) {
+    throw new Error('Invalid data')
+  } else if (tokenValue.length !== 64) {
+    throw new Error('Invalid token value; should be exactly 64 hex digits long (u256)')
+  }
+
+  let customPermissionValue = decimalToHex(calcTokenValue(customPermissionAmount, decimals))
+  if (customPermissionValue.length > 64) {
+    throw new Error('Custom value is larger than u256')
+  }
+
+  customPermissionValue = customPermissionValue.padStart(tokenValue.length, '0')
+  const customTxParamsData = `${signature}${spender}${customPermissionValue}`
+  return customTxParamsData
 }