diff --git a/VAX/vax_cpu.c b/VAX/vax_cpu.c
index 87492442..af9f1c5c 100644
--- a/VAX/vax_cpu.c
+++ b/VAX/vax_cpu.c
@@ -509,7 +509,7 @@ DEVICE cpu_dev = {
 t_stat sim_instr (void)
 {
 volatile int32 opc, cc;                                 /* used by setjmp */
-int32 acc;                                              /* set by setjmp */
+volatile int32 acc;                                     /* set by setjmp */
 int abortval;
 t_stat r;