diff --git a/index.d.ts b/index.d.ts
index 2d447f51..11c7fda0 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -65,6 +65,7 @@ export declare class Peripheral extends events.EventEmitter {
     connectable: boolean;
     advertisement: Advertisement;
     rssi: number;
+    mtu: number | null;
     services: Service[];
     state: 'error' | 'connecting' | 'connected' | 'disconnecting' | 'disconnected';
 
diff --git a/lib/noble.js b/lib/noble.js
index b396e01f..e4bb5133 100644
--- a/lib/noble.js
+++ b/lib/noble.js
@@ -587,7 +587,7 @@ Noble.prototype.onHandleNotify = function (peripheralUuid, handle, data) {
 
 Noble.prototype.onMtu = function (peripheralUuid, mtu) {
   const peripheral = this._peripherals[peripheralUuid];
-  if (peripheral && peripheral.mtu && mtu) peripheral.mtu = mtu;
+  if (peripheral && mtu) peripheral.mtu = mtu;
 };
 
 module.exports = Noble;
diff --git a/test/noble.test.js b/test/noble.test.js
index 239f5b23..7de9261c 100644
--- a/test/noble.test.js
+++ b/test/noble.test.js
@@ -1508,25 +1508,26 @@ describe('noble', () => {
     });
   });
 
-  it('onMtu - should update peripheral mtu', () => {
+  it('onMtu - should update peripheral mtu when set before already', () => {
     const peripheral = {
-      mtu: 'nan'
+      mtu: 234
     };
 
     noble._peripherals = { uuid: peripheral };
-    noble.onMtu('uuid', 'mtu');
+    noble.onMtu('uuid', 123);
 
-    should(peripheral).deepEqual({ mtu: 'mtu' });
+    should(peripheral).deepEqual({ mtu: 123 });
   });
 
-  it('onMtu - should not update peripheral mtu', () => {
+  it('onMtu - should update peripheral mtu too when empty', () => {
     const peripheral = {
+      mtu: null
     };
 
     noble._peripherals = { uuid: peripheral };
-    noble.onMtu('uuid', 'mtu');
+    noble.onMtu('uuid', 123);
 
-    should(peripheral).deepEqual({ });
+    should(peripheral).deepEqual({ mtu: 123 });
   });
 
   describe('onIncludedServicesDiscover', () => {