diff --git a/pw_sync_threadx/public/pw_sync_threadx/interrupt_spin_lock_native.h b/pw_sync_threadx/public/pw_sync_threadx/interrupt_spin_lock_native.h
index 6b6d3f7..01e07ab 100644
--- a/pw_sync_threadx/public/pw_sync_threadx/interrupt_spin_lock_native.h
+++ b/pw_sync_threadx/public/pw_sync_threadx/interrupt_spin_lock_native.h
@@ -19,7 +19,7 @@
 
 struct NativeInterruptSpinLock {
   enum class State {
-    kUnlocked = 0,
+    kUnlocked = 0,  // This must be 0 to ensure it is bss eligible.
     kLockedFromInterrupt = 1,
     kLockedFromThread = 2,
   };