diff --git a/scripts/update-slave-firmware.js b/scripts/update-slave-firmware.js
index 9548e87..0fbf455 100755
--- a/scripts/update-slave-firmware.js
+++ b/scripts/update-slave-firmware.js
@@ -8,7 +8,7 @@ program
     .usage('update-slave-firmware <firmware-image>')
     .parse(process.argv)
 
-const firmwareImage = program.args[0];
+let firmwareImage = program.args[0];
 
 if (!firmwareImage) {
     echo('No firmware image specified');
@@ -25,8 +25,8 @@ if (!test('-f', firmwareImage)) {
     exit(1);
 }
 
-var usbDir = '../../../lib/agent/packages/usb';
-var usbBinding = usbDir + '/node_modules/usb/build/Release/usb_bindings.node';
+let usbDir = '../../../lib/agent/packages/usb';
+let usbBinding = usbDir + '/node_modules/usb/build/Release/usb_bindings.node';
 
 let blhostPath;
 switch (process.platform) {
@@ -45,8 +45,8 @@ switch (process.platform) {
         break;
 }
 
-var blhostUsb = `../../../lib/bootloader/bin/Tools/blhost/${blhostPath} --usb 0x1d50,0x6121`;
-var blhostBuspal = blhostUsb + ' --buspal i2c,0x10,100k';
+let blhostUsb = `../../../lib/bootloader/bin/Tools/blhost/${blhostPath} --usb 0x1d50,0x6121`;
+let blhostBuspal = blhostUsb + ' --buspal i2c,0x10,100k';
 
 config.verbose = true;