diff --git a/PDP10/pdp10_cpu.c b/PDP10/pdp10_cpu.c
index 8a24bfed..21098b5e 100644
--- a/PDP10/pdp10_cpu.c
+++ b/PDP10/pdp10_cpu.c
@@ -197,6 +197,7 @@ jmp_buf save_env;
 int32 hst_p = 0;                                        /* history pointer */
 int32 hst_lnt = 0;                                      /* history length */
 InstHistory *hst = NULL;                                /* instruction history */
+int32 apr_serial = -1;									/* CPU Serial number */
 
 /* Forward and external declarations */
 
@@ -205,6 +206,9 @@ t_stat cpu_dep (t_value val, t_addr addr, UNIT *uptr, int32 sw);
 t_stat cpu_reset (DEVICE *dptr);
 t_stat cpu_set_hist (UNIT *uptr, int32 val, char *cptr, void *desc);
 t_stat cpu_show_hist (FILE *st, UNIT *uptr, int32 val, void *desc);
+t_stat cpu_set_serial (UNIT *uptr, int32 val, char *cptr, void *desc);
+t_stat cpu_show_serial (FILE *st, UNIT *uptr, int32 val, void *desc);
+
 d10 adjsp (d10 val, a10 ea);
 void ibp (a10 ea, int32 pflgs);
 d10 ldb (a10 ea, int32 pflgs);
@@ -400,6 +404,7 @@ MTAB cpu_mod[] = {
       NULL, &show_iospace },
     { MTAB_XTD|MTAB_VDV|MTAB_NMO|MTAB_SHP, 0, "HISTORY", "HISTORY",
       &cpu_set_hist, &cpu_show_hist },
+	{ MTAB_XTD|MTAB_VDV|MTAB_VALR, 0, "SERIAL", "SERIAL", &cpu_set_serial, &cpu_show_serial },
     { 0 }
     };
 
@@ -2104,8 +2109,14 @@ return;
 
 t_bool aprid (a10 ea, int32 prv)
 {
-Write (ea, (Q_ITS)? UC_AIDITS: UC_AIDDEC, prv);
-return FALSE;
+	d10 value = (Q_ITS)? UC_AIDITS: UC_AIDDEC;
+	if( (apr_serial == -1) || (!Q_ITS && apr_serial < 4096) )
+		value |= (Q_ITS)? UC_SERITS: UC_SERDEC;
+	else
+		value |= apr_serial;
+
+	Write (ea, value, prv);
+	return FALSE;
 }
 
 /* Checked against KS10 ucode */
@@ -2419,3 +2430,34 @@ for (k = 0; k < lnt; k++) {                             /* print specified */
     }                                                   /* end for */
 return SCPE_OK;
 }
+
+/* Set serial */
+
+t_stat cpu_set_serial (UNIT *uptr, int32 val, char *cptr, void *desc)
+{
+int32 lnt;
+t_stat r;
+
+if (cptr == NULL) {
+    apr_serial = -1;
+	return SCPE_OK;
+    }
+lnt = (int32) get_uint (cptr, 10, 077777, &r);
+if ((r != SCPE_OK) || (lnt <= 0) || (!Q_ITS && lnt < 4096))
+    return SCPE_ARG;
+apr_serial = lnt & 077777;
+return SCPE_OK;
+}
+
+/* Show serial */
+
+t_stat cpu_show_serial (FILE *st, UNIT *uptr, int32 val, void *desc)
+{
+fprintf (st, "Serial: " );
+if( (apr_serial == -1) || (!Q_ITS && apr_serial < 4096) ) {
+	fprintf (st, "%d (default)", (Q_ITS)? UC_SERITS: UC_SERDEC);
+	return SCPE_OK;
+}
+fprintf (st, "%d", apr_serial);
+return SCPE_OK;
+}
diff --git a/PDP10/pdp10_defs.h b/PDP10/pdp10_defs.h
index fac99a78..a88c92f8 100644
--- a/PDP10/pdp10_defs.h
+++ b/PDP10/pdp10_defs.h
@@ -476,8 +476,9 @@ typedef t_int64         d10;                            /* PDP-10 data (36b) */
 #define UC_SERDEC       4097                            /* serial number */
 #define UC_SERITS       1729
 #define UC_AIDDEC       (UC_INHCST | UC_UBABLT | UC_KIPAGE | UC_KLPAGE | \
-                         UC_VERDEC | UC_SERDEC)
-#define UC_AIDITS       (UC_KIPAGE | UC_VERITS | UC_SERITS)
+                         UC_VERDEC)
+#define UC_AIDITS       (UC_KIPAGE | UC_VERITS)
+
 #define UC_HSBDEC       0376000                         /* DEC initial HSB */
 #define UC_HSBITS       0000500                         /* ITS initial HSB */