diff --git a/.gitignore b/.gitignore
index e20d12c..e0e7f16 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,6 +4,7 @@ node_modules/
 coverage/
 .nyc_output/
 yarn.lock
+package-lock.json
 *.tgz
 *.lock
 *.swp
diff --git a/src/ISO8583.ts b/src/ISO8583.ts
index a2116e2..d592e3a 100644
--- a/src/ISO8583.ts
+++ b/src/ISO8583.ts
@@ -24,8 +24,8 @@ import addStaticMetaData from './pack/addStaticMetaData';
  */
 export default class ISO8583 extends ISO8583Base {
   dataString: string = '';
-  constructor(message?: Types.ISOMessageT, customFormats?: Types.CustomFormatsT, requiredFieldsSchema?: any) {
-    super(message, customFormats, requiredFieldsSchema);
+  constructor(message?: Types.ISOMessageT, customFormats?: Types.CustomFormatsT, requiredFieldsSchema?: any, config?: Types.KeyValueT) {
+    super(message, customFormats, requiredFieldsSchema, config);
   }
 
   static getFieldDescription(
@@ -756,11 +756,11 @@ export default class ISO8583 extends ISO8583Base {
         return state;
       } else {
         return (
-          header +
-          jxon.jsToString({
-            MsgType: this.MsgType,
-            Fields: this.fields,
-          })
+            header +
+            jxon.jsToString({
+              MsgType: this.MsgType,
+              Fields: this.fields,
+            })
         );
       }
     }
diff --git a/src/ISO8583Base.ts b/src/ISO8583Base.ts
index 6f474e6..9a09f0d 100644
--- a/src/ISO8583Base.ts
+++ b/src/ISO8583Base.ts
@@ -93,8 +93,12 @@ export default class ISO8583Base {
     message?: ISO8583MessageType,
     customFormats?: Types.CustomFormatsT,
     requiredFieldsSchema?: Types.RequiredFieldSchemaT,
+    config?: Types.KeyValueT,
   ) {
     this.formats = customFormats || {};
+    if (config) {
+      this.config = config;
+    }
     this.hasSpecialFields = false;
     if (Buffer.isBuffer(message)) {
       this.BufferMsg = message;
diff --git a/src/unpack/unpack_0_127.ts b/src/unpack/unpack_0_127.ts
index db41f1a..308d589 100644
--- a/src/unpack/unpack_0_127.ts
+++ b/src/unpack/unpack_0_127.ts
@@ -30,12 +30,11 @@ export default function (incoming: Buffer, isoJSON: Types.KeyValueStringT, confi
     const bitmap = T.getHex(slice).split('').map(Number);
 
     let thisBuff = incoming.slice(bitmapEnd, incoming.byteLength);
-    for (let i = 1; i < bitmap.length; i++) {
-      if (bitmap[i] === 1) {
+    for (let field = 2; field <= bitmap.length; field++) {
+      if (bitmap[field - 1] === 1) {
         // format defined
-        const field = i + 1;
         const this_format = this.formats[field] || formats[field];
-        if (field === 127) {
+        if (!config.custom127Encoding && field === 127) {
           const get127Exts = this.unpack_127_1_63(thisBuff, isoJSON);
           if (get127Exts.error) {
             return get127Exts;
@@ -64,17 +63,28 @@ export default function (incoming: Buffer, isoJSON: Types.KeyValueStringT, confi
             if (thisLen === 0) {
               return T.toErrorObject(['field ', field, ' format not implemented']);
             } else {
-              const len = thisBuff.slice(0, thisLen).toString();
-              thisBuff = thisBuff.slice(thisLen, thisBuff.byteLength);
-              isoJSON[field] = thisBuff.slice(0, Number(len)).toString();
-              thisBuff = thisBuff.slice(Number(len), thisBuff.byteLength);
+              const lenBuff: Buffer = thisBuff.subarray(0, thisLen);
+              const lenString: string = lenBuff.toString();
+              let len: number = Number(lenString);
+              if (isNaN(len)) { // with certain lengths you get NAN and readUIntBE seems to work in those cases, not sure why...
+                len = lenBuff.readUIntBE(0, thisLen);
+              }
+              thisBuff = thisBuff.subarray(thisLen, thisBuff.byteLength);
+
+              let encoding: string = 'hex';
+              if (field === 127 && config.custom127Encoding) {
+                encoding = config.custom127Encoding;
+              } else if (config.bitmapEncoding) {
+                encoding = config.bitmapEncoding;
+              }
+              isoJSON[field] = thisBuff.subarray(0, len).toString(encoding);
+              thisBuff = thisBuff.subarray(Number(len), thisBuff.byteLength);
             }
           }
         } else return T.toErrorObject(['field ', field, ' format not implemented']);
       }
     }
 
-    this.remainingBuffer = thisBuff;
     return isoJSON;
   } else return T.toErrorObject(['expecting buffer but got ', typeof incoming]);
 };