diff --git a/PDP11/pdp11_xq.c b/PDP11/pdp11_xq.c
index f167d5b5..7a1011b9 100644
--- a/PDP11/pdp11_xq.c
+++ b/PDP11/pdp11_xq.c
@@ -2088,7 +2088,7 @@ void xqb_read_callback(int status)
 
 void xq_sw_reset(CTLR* xq)
 {
-  const uint16 set_bits = XQ_CSR_XL | XQ_CSR_RL;
+  uint16 set_bits = XQ_CSR_XL | XQ_CSR_RL;
   int i;
 
   sim_debug(DBG_TRC, xq->dev, "xq_sw_reset()\n");
@@ -2100,6 +2100,11 @@ void xq_sw_reset(CTLR* xq)
     xq->var->iba = xq->var->srr = 0;
   }
 
+  /* Old DEQNA firmware also enabled interrupts and */
+  /* the Ultrix 1.X driver counts on that behavior */  
+  if ((xq->var->type == XQ_T_DEQNA) && xq->dib->vec && (ULTRIX1X))
+    set_bits |= XQ_CSR_IE;
+
   /* reset csr bits */
   xq_csr_set_clr(xq, set_bits, (uint16) ~set_bits);
 
diff --git a/PDP11/pdp11_xq.h b/PDP11/pdp11_xq.h
index 4d1ba1bd..6ed011ee 100644
--- a/PDP11/pdp11_xq.h
+++ b/PDP11/pdp11_xq.h
@@ -75,12 +75,14 @@
 extern int32 PSL;                                       /* PSL */
 extern int32 fault_PC;                                  /* fault PC */
 extern int32 int_req[IPL_HLVL];
-
+uint32 cpu_idle_mask;                                   /* idle mask (OS type) */
+#define ULTRIX1X (cpu_idle_mask&VAX_IDLE_ULT1X)
 #else                                                   /* PDP-11 version */
 #include "pdp11_defs.h"
 #define XQ_RDX          8
 #define XQ_WID          16
 extern int32 int_req[IPL_HLVL];
+#define ULTRIX1X 0
 #endif
 
 #include "sim_ether.h"
diff --git a/VAX/vax_cpu.c b/VAX/vax_cpu.c
index f9b9eef8..b5a7d6ee 100644
--- a/VAX/vax_cpu.c
+++ b/VAX/vax_cpu.c
@@ -2541,6 +2541,11 @@ for ( ;; ) {
         temp = op_ffs (r, op1);                         /* find first 1 */
         WRITE_L (op0 + temp);                           /* store result */
         cc = r? 0: CC_Z;                                /* set cc's */
+        if ((cc == CC_Z) &&                             /* No set bits found? */
+            (cpu_idle_mask & VAX_IDLE_ULT1X) &&         /* running Ultrix 1.X" */
+            (PSL_GETIPL (PSL) == 0x0) &&                /*  at IPL 0? */
+            (fault_PC & 0x80000000))                    /* in system space? */
+            cpu_idle();                                 /* idle loop */
         break;
 
     case FFC:
@@ -3527,11 +3532,12 @@ static struct os_idle os_tab[] = {
     { "NETBSD", VAX_IDLE_BSDNEW },
     { "ULTRIX", VAX_IDLE_ULT },
     { "ULTRIXOLD", VAX_IDLE_ULTOLD },
+    { "ULTRIX-1.X", VAX_IDLE_ULT1X },
     { "OPENBSDOLD", VAX_IDLE_QUAD },
     { "OPENBSD", VAX_IDLE_BSDNEW },
     { "QUASIJARUS", VAX_IDLE_QUAD },
     { "32V", VAX_IDLE_QUAD },
-    { "ALL", VAX_IDLE_VMS|VAX_IDLE_ULTOLD|VAX_IDLE_ULT|VAX_IDLE_QUAD|VAX_IDLE_BSDNEW },
+    { "ALL", VAX_IDLE_VMS|VAX_IDLE_ULTOLD|VAX_IDLE_ULT|VAX_IDLE_ULT1X|VAX_IDLE_QUAD|VAX_IDLE_BSDNEW },
     { NULL, 0 }
     };
 
diff --git a/VAX/vax_defs.h b/VAX/vax_defs.h
index 893a91c7..3ede6806 100644
--- a/VAX/vax_defs.h
+++ b/VAX/vax_defs.h
@@ -719,10 +719,11 @@ enum opcodes {
             if (((uint32) s1) < ((uint32) s2)) cc = cc | CC_C
 
 #define VAX_IDLE_VMS        0x01
-#define VAX_IDLE_ULT        0x02
-#define VAX_IDLE_ULTOLD     0x04
-#define VAX_IDLE_QUAD       0x08
-#define VAX_IDLE_BSDNEW     0x10
+#define VAX_IDLE_ULT        0x02    /* Ultrix more recent versions */
+#define VAX_IDLE_ULTOLD     0x04    /* Ultrix older versions */
+#define VAX_IDLE_ULT1X      0x08    /* Ultrix 1.x */
+#define VAX_IDLE_QUAD       0x10
+#define VAX_IDLE_BSDNEW     0x20
 extern uint32 cpu_idle_mask;                            /* idle mask */
 void cpu_idle (void);