diff --git a/VAX/vax860_stddev.c b/VAX/vax860_stddev.c
index c656349e..d6a1c1da 100644
--- a/VAX/vax860_stddev.c
+++ b/VAX/vax860_stddev.c
@@ -193,6 +193,7 @@
                          RLDS_VCK+RLDS_DSE)             /* errors bits */
 
 int32 tti_csr = 0;                                      /* control/status */
+uint32 tti_buftime;                                     /* time input character arrived */
 int32 tti_buf = 0;                                      /* buffer */
 int32 tti_int = 0;                                      /* interrupt */
 int32 tto_csr = 0;                                      /* control/status */
@@ -590,13 +591,16 @@ switch (line) {
 
     case ID_CT:                                         /* console terminal */
         sim_clock_coschedule (uptr, tmxr_poll);         /* continue poll */
-        if ((tti_csr & CSR_DONE) == 0) {                /* prev data taken? */
-            if ((c = sim_poll_kbd ()) < SCPE_KFLAG)     /* no char or error? */
-                return c;
-            if (c & SCPE_BREAK)                         /* break? */
-                tti_buf = 0;
-            else tti_buf = sim_tt_inpcvt (c, TT_GET_MODE (uptr->flags));
-            }
+        if ((tti_csr & CSR_DONE) &&                     /* input still pending and < 500ms? */
+            ((sim_os_msec () - tti_buftime) < 500))
+             return SCPE_OK;
+        if ((c = sim_poll_kbd ()) < SCPE_KFLAG)         /* no char or error? */
+            return c;
+        if (c & SCPE_BREAK)                             /* break? */
+            tti_buf = 0;
+        else
+            tti_buf = sim_tt_inpcvt (c, TT_GET_MODE (uptr->flags));
+        tti_buftime = sim_os_msec ();
         break;
 
     case ID_LC:                                         /* logical console */