diff --git a/PDP10/pdp10_cpu.c b/PDP10/pdp10_cpu.c
index 3ea20fe6..9eb3c418 100644
--- a/PDP10/pdp10_cpu.c
+++ b/PDP10/pdp10_cpu.c
@@ -2212,8 +2212,11 @@ if (ea & APR_SENB)                                      /* set enables? */
     apr_enb = apr_enb | bits;
 if (ea & APR_CENB)                                      /* clear enables? */
     apr_enb = apr_enb & ~bits;
-if (ea & APR_CFLG)                                      /* clear flags? */
+if (ea & APR_CFLG) {                                    /* clear flags? */
+    if ((bits & APRF_TIM) && (apr_flg & APRF_TIM)
+        sim_rtcn_tick_ack (30, 0);
     apr_flg = apr_flg & ~bits;
+    }
 if (ea & APR_SFLG)                                      /* set flags? */
     apr_flg = apr_flg | bits;
 if (apr_flg & APRF_ITC) {                               /* interrupt console? */