diff --git a/lib/encoding.js b/lib/encoding.js
index 7a04bf8..a750282 100644
--- a/lib/encoding.js
+++ b/lib/encoding.js
@@ -274,12 +274,6 @@ if (typeof module !== "undefined" && module.exports) {
   /** @const */
   var finished = -1;
 
-  /** @const */
-  var error_mode_replacement = false;
-
-  /** @const */
-  var error_mode_fatal = true;
-
   /**
    * @param {boolean} fatal If true, decoding errors raise an exception.
    * @param {number=} opt_code_point Override the standard fallback code point.
@@ -1008,8 +1002,8 @@ if (typeof module !== "undefined" && module.exports) {
     this._ignoreBOM = false;
     /** @private @type {boolean} */
     this._BOMseen = false;
-    /** @private @type {boolean} */
-    this._error_mode = error_mode_replacement;
+    /** @private @type {string} */
+    this._error_mode = 'replacement';
     /** @private @type {boolean} */
     this._do_not_flush = false;
 
@@ -1035,7 +1029,7 @@ if (typeof module !== "undefined" && module.exports) {
     // 5. If options's fatal member is true, set dec's error mode to
     // fatal.
     if (Boolean(options['fatal']))
-      dec._error_mode = error_mode_fatal;
+      dec._error_mode = 'fatal';
 
     // 6. If options's ignoreBOM member is true, set dec's ignore BOM
     // flag.
@@ -1045,7 +1039,7 @@ if (typeof module !== "undefined" && module.exports) {
     // For pre-ES5 runtimes:
     if (!Object.defineProperty) {
       this.encoding = dec._encoding.name;
-      this.fatal = dec._error_mode;
+      this.fatal = dec._error_mode === 'fatal';
       this.ignoreBOM = dec._ignoreBOM;
     }
 
@@ -1064,7 +1058,7 @@ if (typeof module !== "undefined" && module.exports) {
     // is fatal, and false otherwise.
     Object.defineProperty(TextDecoder.prototype, 'fatal', {
       /** @this {TextDecoder} */
-      get: function() { return this._error_mode === error_mode_fatal; }
+      get: function() { return this._error_mode === 'fatal'; }
     });
 
     // The ignoreBOM attribute's getter must return true if ignore
@@ -1099,7 +1093,8 @@ if (typeof module !== "undefined" && module.exports) {
     // encoding's decoder, set stream to a new stream, and unset the
     // BOM seen flag.
     if (!this._do_not_flush) {
-      this._decoder = decoders[this._encoding.name]({fatal: this._error_mode});
+      this._decoder = decoders[this._encoding.name]({
+        fatal: this._error_mode === 'fatal'});
       this._BOMseen = false;
     }
 
@@ -1228,8 +1223,8 @@ if (typeof module !== "undefined" && module.exports) {
     // Non-standard
     /** @private @type {boolean} */
     this._do_not_flush = false;
-    /** @private @type {boolean} */
-    this._fatal = Boolean(options['fatal']);
+    /** @private @type {string} */
+    this._fatal = Boolean(options['fatal']) ? 'fatal' : 'replacement';
 
     // 1. Let encoding be the result of getting an encoding from utfLabel.
     var encoding = getEncoding(label);
@@ -1283,7 +1278,8 @@ if (typeof module !== "undefined" && module.exports) {
     // permitted for encoding (i.e. UTF-8, UTF-16) are stateful when
     // the input is a USVString so streaming is not necessary.
     if (!this._do_not_flush)
-      this._encoder = encoders[this._encoding.name]({fatal: this._fatal});
+      this._encoder = encoders[this._encoding.name]({
+        fatal: this._fatal === 'fatal'});
     this._do_not_flush = Boolean(options['stream']);
 
     // 1. Convert input to a stream.