diff --git a/src/PIC.cc b/src/PIC.cc
index 474fb59..448e497 100644
--- a/src/PIC.cc
+++ b/src/PIC.cc
@@ -90,6 +90,7 @@ PIC::remap(uint8_t pic1Offset,
 
 void
 PIC::endOfInterrupt(uint8_t irq)
+    const
 {
     /*
      * Notifying the PICs that an interrupt has been completed uses OCW2 on the
diff --git a/src/PIC.hh b/src/PIC.hh
index 44fc845..0168904 100644
--- a/src/PIC.hh
+++ b/src/PIC.hh
@@ -56,7 +56,7 @@ struct PIC
      * interrupt has been handled. This _must_ be done after the kernel has
      * handled a hardware interrupt.
      */
-    void endOfInterrupt(uint8_t irq);
+    void endOfInterrupt(uint8_t irq) const;
 
     /**
      * Enable or disable the given IRQ. This is done by setting a mask bit in