diff --git a/scp.c b/scp.c
index e0736cd1..d0578584 100644
--- a/scp.c
+++ b/scp.c
@@ -10790,7 +10790,7 @@ return _sim_activate_after_abs (uptr, usec_delay);
 
 t_stat _sim_activate_after_abs (UNIT *uptr, double usec_delay)
 {
-AIO_VALIDATE;                   /* Can't call asynchronously */
+AIO_VALIDATE(uptr);             /* Can't call asynchronously */
 sim_cancel (uptr);
 return _sim_activate_after (uptr, usec_delay);
 }
@@ -10807,8 +10807,8 @@ return _sim_activate_after (uptr, usec_delay);
 
 t_stat _sim_activate_after (UNIT *uptr, double usec_delay)
 {
-AIO_VALIDATE;                   /* Can't call asynchronously */
-if (sim_is_active (uptr))                               /* already active? */
+AIO_VALIDATE(uptr);             /* Can't call asynchronously */
+if (sim_is_active (uptr))       /* already active? */
     return SCPE_OK;
 return sim_timer_activate_after (uptr, usec_delay);
 }
@@ -10826,7 +10826,7 @@ t_stat sim_cancel (UNIT *uptr)
 {
 UNIT *cptr, *nptr;
 
-AIO_VALIDATE;
+AIO_VALIDATE(uptr);
 if ((uptr->cancel) && uptr->cancel (uptr))
     return SCPE_OK;
 if (uptr->dynflags & UNIT_TMR_UNIT)
@@ -10881,7 +10881,7 @@ return SCPE_OK;
 
 t_bool sim_is_active (UNIT *uptr)
 {
-AIO_VALIDATE;
+AIO_VALIDATE(uptr);
 AIO_UPDATE_QUEUE;
 return (((uptr->next) || AIO_IS_ACTIVE(uptr) || ((uptr->dynflags & UNIT_TMR_UNIT) ? sim_timer_is_active (uptr) : FALSE)) ? TRUE : FALSE);
 }
@@ -10917,7 +10917,7 @@ int32 sim_activate_time (UNIT *uptr)
 {
 int32 accum;
 
-AIO_VALIDATE;
+AIO_VALIDATE(uptr);
 accum = _sim_timer_activate_time (uptr);
 if (accum >= 0)
     return accum;
@@ -10930,7 +10930,7 @@ UNIT *cptr;
 int32 accum;
 double result;
 
-AIO_VALIDATE;
+AIO_VALIDATE(uptr);
 result = sim_timer_activate_time_usecs (uptr);
 if (result >= 0)
     return result;
diff --git a/sim_defs.h b/sim_defs.h
index fc9293c9..834bcf97 100644
--- a/sim_defs.h
+++ b/sim_defs.h
@@ -1256,7 +1256,12 @@ extern int32 sim_asynch_inst_latency;
       return SCPE_OK;                                                  \
     } else (void)0
 #endif /* USE_AIO_INTRINSICS */
-#define AIO_VALIDATE if (!pthread_equal ( pthread_self(), sim_asynch_main_threadid )) {sim_printf("Improper thread context for operation in %s line %d\n", __FILE__, __LINE__); abort();}
+#define AIO_VALIDATE(uptr)                                             \
+    if (!pthread_equal ( pthread_self(), sim_asynch_main_threadid )) { \
+      sim_printf("Improper thread context for operation on %s in %s line %d\n", \
+                   sim_uname(uptr), __FILE__, __LINE__);               \
+      abort();                                                         \
+      } else (void)0
 #define AIO_CHECK_EVENT                                                \
     if (0 > --sim_asynch_check) {                                      \
       AIO_UPDATE_QUEUE;                                                \
@@ -1272,7 +1277,7 @@ extern int32 sim_asynch_inst_latency;
 #define AIO_QUEUE_MODE "Asynchronous I/O is not available"
 #define AIO_UPDATE_QUEUE
 #define AIO_ACTIVATE(caller, uptr, event_time)
-#define AIO_VALIDATE
+#define AIO_VALIDATE(uptr)
 #define AIO_CHECK_EVENT
 #define AIO_INIT
 #define AIO_MAIN_THREAD TRUE
diff --git a/sim_disk.c b/sim_disk.c
index 91076565..66a62e92 100644
--- a/sim_disk.c
+++ b/sim_disk.c
@@ -1996,7 +1996,7 @@ if (!(uptr->flags & UNIT_ATT))                          /* attached? */
 sim_debug_unit (ctx->dbit, uptr, "sim_disk_reset(unit=%d)\n", (int)(uptr-ctx->dptr->units));
 
 _sim_disk_io_flush(uptr);
-AIO_VALIDATE;
+AIO_VALIDATE(uptr);
 AIO_UPDATE_QUEUE;
 return SCPE_OK;
 }
diff --git a/sim_tape.c b/sim_tape.c
index bc52bd23..3bbd2275 100644
--- a/sim_tape.c
+++ b/sim_tape.c
@@ -2439,7 +2439,7 @@ if (ctx == NULL)                                        /* if not properly attac
 sim_debug_unit (ctx->dbit, uptr, "sim_tape_reset(unit=%d)\n", (int)(uptr-ctx->dptr->units));
 
 _sim_tape_io_flush(uptr);
-AIO_VALIDATE;
+AIO_VALIDATE(uptr);
 AIO_UPDATE_QUEUE;
 return SCPE_OK;
 }
diff --git a/sim_timer.c b/sim_timer.c
index 0e99f746..d31979bf 100644
--- a/sim_timer.c
+++ b/sim_timer.c
@@ -2508,7 +2508,7 @@ return inst_per_sec;
 
 t_stat sim_timer_activate (UNIT *uptr, int32 interval)
 {
-AIO_VALIDATE;
+AIO_VALIDATE(uptr);
 return sim_timer_activate_after (uptr, (double)((interval * 1000000.0) / sim_timer_inst_per_sec ()));
 }
 
@@ -2519,7 +2519,7 @@ int inst_delay, tmr;
 double inst_delay_d, inst_per_usec;
 t_stat stat;
 
-AIO_VALIDATE;
+AIO_VALIDATE(uptr);
 /* If this is a clock unit, we need to schedule the related timer unit instead */
 for (tmr=0; tmr<=SIM_NTIMERS; tmr++)
     if (sim_clock_unit[tmr] == uptr) {
diff --git a/sim_tmxr.c b/sim_tmxr.c
index 1e8f027c..29cd88d5 100644
--- a/sim_tmxr.c
+++ b/sim_tmxr.c
@@ -4260,7 +4260,7 @@ return _sim_activate (uptr, interval);
 
 t_stat tmxr_activate_abs (UNIT *uptr, int32 interval)
 {
-AIO_VALIDATE;                   /* Can't call asynchronously */
+AIO_VALIDATE(uptr);             /* Can't call asynchronously */
 sim_cancel (uptr);
 return tmxr_activate (uptr, interval);
 }