diff --git a/lib/utils/bignumber/formatter.js b/lib/utils/bignumber/formatter.js
index 748207aac..ae8265714 100644
--- a/lib/utils/bignumber/formatter.js
+++ b/lib/utils/bignumber/formatter.js
@@ -1,4 +1,7 @@
 'use strict';
+
+var objectUtils = require('../object');
+
 /**
  * Convert a BigNumber to a formatted string representation.
  *
@@ -107,7 +110,7 @@ exports.format = function (value, options) {
       // TODO: clean up some day. Deprecated since: 2018-01-24
       // @deprecated upper and lower are replaced with upperExp and lowerExp since v4.0.0
       if (options && options.exponential && (options.exponential.lower !== undefined || options.exponential.upper !== undefined)) {
-        var fixedOptions = Object.assign({}, options);
+        var fixedOptions = objectUtils.map(options, function (x) { return x; });
         fixedOptions.exponential = undefined;
         if (options.exponential.lower !== undefined) {
           fixedOptions.lowerExp = Math.round(Math.log(options.exponential.lower) / Math.LN10);
diff --git a/lib/utils/number.js b/lib/utils/number.js
index 1ffb49dfd..8bfc12cfc 100644
--- a/lib/utils/number.js
+++ b/lib/utils/number.js
@@ -1,5 +1,7 @@
 'use strict';
 
+var objectUtils = require('./object');
+
 /**
  * @typedef {{sign: '+' | '-' | '', coefficients: number[], exponent: number}} SplitValue
  */
@@ -162,7 +164,7 @@ exports.format = function(value, options) {
       // TODO: clean up some day. Deprecated since: 2018-01-24
       // @deprecated upper and lower are replaced with upperExp and lowerExp since v4.0.0
       if (options && options.exponential && (options.exponential.lower !== undefined || options.exponential.upper !== undefined)) {
-        var fixedOptions = Object.assign({}, options);
+        var fixedOptions = objectUtils.map(options, function(x) { return x; });
         fixedOptions.exponential = undefined;
         if (options.exponential.lower !== undefined) {
           fixedOptions.lowerExp = Math.round(Math.log(options.exponential.lower) / Math.LN10);