--- a/packages/hal/powerpc/arch/current/src/hal_misc.c
+++ b/packages/hal/powerpc/arch/current/src/hal_misc.c
@@ -157,7 +157,7 @@ cyg_hal_exception_handler(HAL_SavedRegis
 }
 
 //---------------------------------------------------------------------------
-// Default ISR
+// Default ISRs
 
 externC cyg_uint32
 hal_default_isr(CYG_ADDRWORD vector, CYG_ADDRWORD data)
@@ -168,6 +168,17 @@ hal_default_isr(CYG_ADDRWORD vector, CYG
     return 0;
 }
 
+// The decrementer default ISR has to do nothing. The reason is that
+// decrementer interrupts cannot be disabled - if a kernel configuration
+// does not use the RTC, but does use external interrupts, the decrementer
+// underflow could cause a CYG_FAIL (as above) even though the user did
+// not expect any decrementer interrupts to happen.
+externC cyg_uint32
+hal_default_decrementer_isr(CYG_ADDRWORD vector, CYG_ADDRWORD data)
+{
+    return 0;
+}
+
 //---------------------------------------------------------------------------
 // Idle thread action