diff --git a/firmware/src/main.rs b/firmware/src/main.rs
index 01f3204..7485af7 100644
--- a/firmware/src/main.rs
+++ b/firmware/src/main.rs
@@ -133,11 +133,22 @@ mod app {
 
         let usb_serial = usbd_serial::SerialPort::new(unsafe { USB_BUS.as_ref().unwrap() });
 
-        let uid = signature::Uid::get();
+        let serial = unsafe {
+            let u_id0 = 0x1FFF_7A10 as *const u32;
+            let u_id2 = 0x1FFF_7A18 as *const u32;
+
+            defmt::debug!("UID0: {:x}", u_id0.read());
+            defmt::debug!("UID2: {:x}", u_id2.read());
+
+            // See https://community.st.com/t5/stm32-mcus-products/usb-bootloader-serial-number/td-p/432148
+            (u_id0.read() as u64 + u_id2.read() as u64) << 16
+                | (u_id2.read() as u64 & 0xFF00) >> 8
+                | (u_id2.read() as u64 & 0x00FF) << 8
+        };
 
         static mut SERIAL: String<16> = String::new();
         unsafe {
-            write!(SERIAL, "{}{:x}{:x}", uid.lot_num(), uid.x(), uid.y()).unwrap();
+            write!(SERIAL, "{:X}", serial).unwrap();
         }
 
         let usb_dev = unsafe {