diff --git a/src/hulk/cpu.d b/src/hulk/cpu.d
index 0edd8dd..aa3af81 100644
--- a/src/hulk/cpu.d
+++ b/src/hulk/cpu.d
@@ -135,37 +135,6 @@ enum uint CPUID_1_ECX_RDRND = 0x4000_0000u;
 enum uint CPUID_1_ECX_HYPERVISOR = 0x8000_0000u;
 /** @} */
 
-/** Interrupt suspend level (0 when interrupts are enabled). */
-private __gshared size_t intr_suspend_level;
-
-/**
- * Suspend interrupts.
- *
- * This function disables interrupts. Calls can be nested and interrupts will
- * be enabled only when the outermost pair of
- * suspend_interrupts()/resume_interrupts() is complete.
- */
-void suspend_interrupts()
-{
-    cli();
-    intr_suspend_level++;
-}
-
-/**
- * Resume interrupts.
- *
- * Calls can be nested and interrupts will be enabled only when the outermost
- * pair of suspend_interrupts()/resume_interrupts() is complete.
- */
-void resume_interrupts()
-{
-    intr_suspend_level--;
-    if (intr_suspend_level == 0)
-    {
-        sti();
-    }
-}
-
 void cli()
 {
     __asm("cli", "");
diff --git a/src/hulk/him.d b/src/hulk/him.d
index 2609afc..23ad3d2 100644
--- a/src/hulk/him.d
+++ b/src/hulk/him.d
@@ -102,6 +102,46 @@ mixin(`private static __gshared extern(C) void function()[N_ISRS] isrs = [`,
         isrs_list(),
         `];`);
 
+/** Interrupt suspend level (0 when interrupts are enabled). */
+private __gshared size_t interrupt_suspend_level;
+
+/** Interrupt nest level (0 when not in an interrupt handler). */
+private __gshared size_t interrupt_level;
+
+/**
+ * Suspend interrupts.
+ *
+ * This function disables interrupts. Calls can be nested and interrupts will
+ * be enabled only when the outermost pair of
+ * suspend_interrupts()/resume_interrupts() is complete.
+ */
+void suspend_interrupts()
+{
+    if (interrupt_level == 0)
+    {
+        cli();
+        interrupt_suspend_level++;
+    }
+}
+
+/**
+ * Resume interrupts.
+ *
+ * Calls can be nested and interrupts will be enabled only when the outermost
+ * pair of suspend_interrupts()/resume_interrupts() is complete.
+ */
+void resume_interrupts()
+{
+    if (interrupt_level == 0)
+    {
+        interrupt_suspend_level--;
+        if (interrupt_suspend_level == 0)
+        {
+            sti();
+        }
+    }
+}
+
 struct Him
 {
     /**
@@ -235,6 +275,7 @@ struct Him
  */
 public extern(C) ulong * isr(ulong vector, ulong * stack_frame)
 {
+    interrupt_level++;
     Thread.current_thread.stack_pointer = stack_frame;
     if ((vector >= INT_APIC_BASE) && (vector < (INT_APIC_BASE + INT_APIC_COUNT)))
     {
@@ -268,5 +309,6 @@ public extern(C) ulong * isr(ulong vector, ulong * stack_frame)
         }
     }
     Thread.current_thread = Thread.current_thread.list_next;
+    interrupt_level--;
     return Thread.current_thread.stack_pointer;
 }