diff --git a/src/extensions/scratch3_ev3/index.js b/src/extensions/scratch3_ev3/index.js
index 41d541d81..667aaf5e8 100644
--- a/src/extensions/scratch3_ev3/index.js
+++ b/src/extensions/scratch3_ev3/index.js
@@ -346,7 +346,7 @@ class EV3Motor {
      */
     coast () {
         if (this._power === 0) return;
-        
+
         const cmd = this._parent.generateCommand(
             Ev3Command.DIRECT_COMMAND_NO_REPLY,
             [
@@ -555,6 +555,9 @@ class EV3 {
      * Called by the runtime when user wants to scan for an EV3 peripheral.
      */
     scan () {
+        if (this._bt) {
+            this._bt.disconnect();
+        }
         this._bt = new BT(this._runtime, this._extensionId, {
             majorDeviceClass: 8,
             minorDeviceClass: 1
@@ -566,17 +569,22 @@ class EV3 {
      * @param {number} id - the id of the peripheral to connect to.
      */
     connect (id) {
-        this._bt.connectPeripheral(id);
+        if (this._bt) {
+            this._bt.connectPeripheral(id);
+        }
     }
 
     /**
      * Called by the runtime when user wants to disconnect from the EV3 peripheral.
      */
     disconnect () {
-        this._bt.disconnect();
         this._clearSensorsAndMotors();
         window.clearInterval(this._pollingIntervalID);
         this._pollingIntervalID = null;
+
+        if (this._bt) {
+            this._bt.disconnect();
+        }
     }
 
     /**
diff --git a/src/extensions/scratch3_microbit/index.js b/src/extensions/scratch3_microbit/index.js
index 03b78b57f..3e880d8cd 100644
--- a/src/extensions/scratch3_microbit/index.js
+++ b/src/extensions/scratch3_microbit/index.js
@@ -205,6 +205,9 @@ class MicroBit {
      * Called by the runtime when user wants to scan for a peripheral.
      */
     scan () {
+        if (this._ble) {
+            this._ble.disconnect();
+        }
         this._ble = new BLE(this._runtime, this._extensionId, {
             filters: [
                 {services: [BLEUUID.service]}
@@ -217,7 +220,9 @@ class MicroBit {
      * @param {number} id - the id of the peripheral to connect to.
      */
     connect (id) {
-        this._ble.connectPeripheral(id);
+        if (this._ble) {
+            this._ble.connectPeripheral(id);
+        }
     }
 
     /**
@@ -225,7 +230,9 @@ class MicroBit {
      */
     disconnect () {
         window.clearInterval(this._timeoutID);
-        this._ble.disconnect();
+        if (this._ble) {
+            this._ble.disconnect();
+        }
     }
 
     /**
diff --git a/src/extensions/scratch3_wedo2/index.js b/src/extensions/scratch3_wedo2/index.js
index 5781781f9..08e54eead 100644
--- a/src/extensions/scratch3_wedo2/index.js
+++ b/src/extensions/scratch3_wedo2/index.js
@@ -570,6 +570,9 @@ class WeDo2 {
      * Called by the runtime when user wants to scan for a WeDo 2.0 peripheral.
      */
     scan () {
+        if (this._ble) {
+            this._ble.disconnect();
+        }
         this._ble = new BLE(this._runtime, this._extensionId, {
             filters: [{
                 services: [BLEService.DEVICE_SERVICE]
@@ -583,7 +586,9 @@ class WeDo2 {
      * @param {number} id - the id of the peripheral to connect to.
      */
     connect (id) {
-        this._ble.connectPeripheral(id);
+        if (this._ble) {
+            this._ble.connectPeripheral(id);
+        }
     }
 
     /**
@@ -598,7 +603,9 @@ class WeDo2 {
             distance: 0
         };
 
-        this._ble.disconnect();
+        if (this._ble) {
+            this._ble.disconnect();
+        }
     }
 
     /**
diff --git a/src/io/ble.js b/src/io/ble.js
index e407a9856..b7b1c460a 100644
--- a/src/io/ble.js
+++ b/src/io/ble.js
@@ -42,7 +42,7 @@ class BLE extends JSONRPCWebSocket {
             this.sendRemoteRequest('discover', this._peripheralOptions)
                 .catch(e => {
                     this._sendRequestError(e);
-                }); // never reached?
+                });
         }
         // TODO: else?
     }
diff --git a/src/io/bt.js b/src/io/bt.js
index 4f2f834eb..ea7ed4557 100644
--- a/src/io/bt.js
+++ b/src/io/bt.js
@@ -42,7 +42,9 @@ class BT extends JSONRPCWebSocket {
             this._availablePeripherals = {};
             this._discoverTimeoutID = window.setTimeout(this._sendDiscoverTimeout.bind(this), 15000);
             this.sendRemoteRequest('discover', this._peripheralOptions)
-                .catch(e => this._sendRequestError(e)); // never reached?
+                .catch(
+                    e => this._sendRequestError(e)
+                );
         }
         // TODO: else?
     }