diff --git a/src/hulk/apic.d b/src/hulk/apic.d
index 6993265..715cfb2 100644
--- a/src/hulk/apic.d
+++ b/src/hulk/apic.d
@@ -17,7 +17,7 @@ struct Apic
     private enum DEFAULT_IO_APIC_ADDRESS = 0xFEC0_0000u;
     private enum uint PERIODIC_MODE = 0x2_0000u;
 
-    private enum ulong IRQ_PIT = 2u;
+    private enum ulong IRQ_PIT = 0u;
     private enum ulong IRQ_RTC = 8u;
 
     /**
@@ -180,6 +180,14 @@ struct Apic
 
                 case Entry.IO_APIC_INTERRUPT_SOURCE_OVERRIDE:
                     Entry2 * e = cast(Entry2 *)entry;
+                    if (e.global_system_interrupt < Idt.INT_APIC_COUNT)
+                    {
+                        irq_redirects[e.irq_source] = cast(ubyte)e.global_system_interrupt;
+                    }
+                    else
+                    {
+                        Klog.writefln("Warning: unexpected interrupt source override global system interrupt value: %u", e.global_system_interrupt);
+                    }
                     if (DEBUG)
                     {
                         Klog.writefln("  Bus %u IRQ %u GSI %u Flags: 0x%x",
@@ -296,8 +304,11 @@ struct Apic
         ApicRegister data;
     }
 
+    alias ISRHandler = void function();
     private static __gshared ApicRegisters * apic_registers;
     private static __gshared IoApicRegisters * io_apic_registers;
+    private static __gshared ISRHandler[Idt.INT_APIC_COUNT] irq_handlers;
+    private static __gshared ubyte[Idt.INT_APIC_COUNT] irq_redirects;
 
     /**
      * Initialize APIC.
@@ -306,6 +317,10 @@ struct Apic
     {
         Klog.writefln("\a3Initializing APIC");
         io_apic_registers = cast(IoApicRegisters *)DEFAULT_IO_APIC_ADDRESS;
+        for (ubyte i = 0u; i < Idt.INT_APIC_COUNT; i++)
+        {
+            irq_redirects[i] = i;
+        }
         MADT * madt = cast(MADT *)Acpi.get_table("APIC");
         madt.scan();
         Klog.writefln("APIC found at %p", apic_registers);
@@ -321,21 +336,23 @@ struct Apic
         apic_registers.lvt_lint[0].value = Idt.INT_APIC_LINT0;
         apic_registers.lvt_lint[1].value = Idt.INT_APIC_LINT1;
         /* Enable PIT interrupt. */
-        configure_io_apic_irq(IRQ_PIT, Idt.INT_APIC_BASE + IRQ_PIT);
+        configure_io_apic_irq(IRQ_PIT, &Pit.isr);
         /* Enable RTC interrupt. */
-        configure_io_apic_irq(IRQ_RTC, Idt.INT_APIC_BASE + IRQ_RTC);
+        configure_io_apic_irq(IRQ_RTC, &Rtc.isr);
     }
 
     /**
      * Configure routing for an I/O APIC IRQ.
      */
-    private static void configure_io_apic_irq(size_t io_apic_irq, size_t interrupt_id)
+    private static void configure_io_apic_irq(size_t orig_irq, ISRHandler isr_handler)
     {
-        ulong entry = interrupt_id;
+        size_t io_apic_irq = irq_redirects[orig_irq];
+        ulong entry = Idt.INT_APIC_BASE + io_apic_irq;
         io_apic_registers.address.value = cast(uint)(0x10u + io_apic_irq * 2u);
         io_apic_registers.data.value = entry & 0xFFFF_FFFFu;
         io_apic_registers.address.value = cast(uint)(0x10u + io_apic_irq * 2u + 1u);
         io_apic_registers.data.value = entry >> 32u;
+        irq_handlers[io_apic_irq] = isr_handler;
     }
 
     /**
@@ -351,19 +368,14 @@ struct Apic
      */
     public static void isr(ulong vector)
     {
-        switch (vector)
+        ulong io_apic_irq = vector - Idt.INT_APIC_BASE;
+        if ((io_apic_irq < Idt.INT_APIC_COUNT) && (irq_handlers[io_apic_irq] != null))
+        {
+            irq_handlers[io_apic_irq]();
+        }
+        else
         {
-        case Idt.INT_APIC_BASE + IRQ_PIT:
-            Pit.isr();
-            break;
-
-        case Idt.INT_APIC_BASE + IRQ_RTC:
-            Rtc.isr();
-            break;
-
-        default:
             Klog.writefln("Unhandled APIC ISR %u", vector);
-            break;
         }
         eoi();
     }