diff --git a/arm/lock.h b/arm/lock.h
index bd6c6b6..ac06a17 100644
--- a/arm/lock.h
+++ b/arm/lock.h
@@ -3,13 +3,11 @@
 #include "aum1_cm1.h"
 
 struct InterruptLock {
-    bool was_locked;
+    uint32_t old_primask;
 
-    InterruptLock() : was_locked(__get_PRIMASK() != 0) { __disable_irq(); }
+    InterruptLock() : old_primask(__get_PRIMASK()) { __disable_irq(); }
 
     ~InterruptLock() {
-        if (!was_locked) {
-            __enable_irq();
-        }
+        __set_PRIMASK(old_primask);
     }
 };