diff --git a/sim_tmxr.c b/sim_tmxr.c
index e020036f..411385af 100644
--- a/sim_tmxr.c
+++ b/sim_tmxr.c
@@ -3130,6 +3130,7 @@ if ((line < 0) || (line >= mp->lines))
 if (mp->ldsc[line].uptr)
     mp->ldsc[line].uptr->dynflags &= ~UNIT_TM_POLL;
 mp->ldsc[line].uptr = uptr_poll;
+mp->ldsc[line].uptr->dynflags |= UNIT_TM_POLL;
 return SCPE_OK;
 }
 
@@ -3163,6 +3164,7 @@ if ((line < 0) || (line >= mp->lines))
 if (mp->ldsc[line].o_uptr)
     mp->ldsc[line].o_uptr->dynflags &= ~UNIT_TM_POLL;
 mp->ldsc[line].o_uptr = uptr_poll;
+mp->ldsc[line].o_uptr->dynflags |= UNIT_TM_POLL;
 return SCPE_OK;
 }