diff --git a/PDP10/ka10_rp.c b/PDP10/ka10_rp.c
index 9a15ec6..18b98f5 100644
--- a/PDP10/ka10_rp.c
+++ b/PDP10/ka10_rp.c
@@ -469,6 +469,7 @@ t_stat rp_devio(uint32 dev, uint64 *data) {
             break;
      }
      df10 = &rp_df10[ctlr];
+     df10->devnum = dev;
      switch(dev & 3) {
      case CONI:
         *data = df10->status & ~(IADR_ATTN|IARD_RAE);
@@ -659,7 +660,7 @@ rp_write(int ctlr, int unit, int reg, uint32 data) {
                 uptr->u3 |= DS_DRY;
                 uptr->u3 &= ~(DS_ATA|CR_GO);
                 rp_attn[ctlr] &= ~(1<<unit);
-                clr_interrupt(rp_dib[ctlr].dev_num);
+                clr_interrupt(df10->devnum);
                 if ((df10->status & IADR_ATTN) != 0 && rp_attn[ctlr] != 0)
                     df10_setirq(df10);
                 break;
@@ -707,7 +708,7 @@ rp_write(int ctlr, int unit, int reg, uint32 data) {
                 rp_attn[ctlr] &= ~(1<<i);
             }
         }
-        clr_interrupt(rp_dib[ctlr].dev_num);
+        clr_interrupt(df10->devnum);
         if (((df10->status & IADR_ATTN) != 0 && rp_attn[ctlr] != 0) ||
              (df10->status & PI_ENABLE))
             df10_setirq(df10);
diff --git a/PDP10/ka10_rs.c b/PDP10/ka10_rs.c
index 9dbea18..8b236d3 100644
--- a/PDP10/ka10_rs.c
+++ b/PDP10/ka10_rs.c
@@ -315,6 +315,7 @@ t_stat rs_devio(uint32 dev, uint64 *data) {
             break;
      }
      df10 = &rs_df10[ctlr];
+     df10->devnum = dev;
      switch(dev & 3) {
      case CONI:
         *data = df10->status & ~(IADR_ATTN|IARD_RAE);
@@ -499,7 +500,7 @@ rs_write(int ctlr, int unit, int reg, uint32 data) {
                 uptr->u3 |= DS_DRY;
                 uptr->u3 &= ~(DS_ATA|CR_GO);
                 rs_attn[ctlr] = 0;
-                clr_interrupt(rs_dib[ctlr].dev_num);
+                clr_interrupt(df10->devnum);
                 for (i = 0; i < 8; i++) {
                     if (rs_unit[(ctlr * 8) + i].u3 & DS_ATA)
                        rs_attn[ctlr] = 1;
@@ -538,7 +539,7 @@ rs_write(int ctlr, int unit, int reg, uint32 data) {
             if (rs_unit[(ctlr * 8) + i].u3 & DS_ATA)
                rs_attn[ctlr] = 1;
         }
-        clr_interrupt(rs_dib[ctlr].dev_num);
+        clr_interrupt(df10->devnum);
         if (((df10->status & IADR_ATTN) != 0 && rs_attn[ctlr] != 0) ||
              (df10->status & PI_ENABLE))
             df10_setirq(df10);
diff --git a/PDP10/ka10_tu.c b/PDP10/ka10_tu.c
index 0e27be4..0c34a0b 100644
--- a/PDP10/ka10_tu.c
+++ b/PDP10/ka10_tu.c
@@ -300,6 +300,7 @@ t_stat tu_devio(uint32 dev, uint64 *data) {
             break;
      }
      df10 = &tu_df10[ctlr];
+     df10->devnum = dev;
      switch(dev & 3) {
      case CONI:
         *data = df10->status & ~(IADR_ATTN|IARD_RAE);
@@ -498,7 +499,7 @@ tu_write(int ctlr, int unit, int reg, uint32 data) {
                 uptr->u3 &= ~(CS_ATA|CR_GO|CS_TM);
                 uptr->u5 = 0;
                 tu_attn[ctlr] = 0;
-                clr_interrupt(tu_dib[ctlr].dev_num);
+                clr_interrupt(df10->devnum);
                 for (i = 0; i < 8; i++) {
                     if (tu_unit[(ctlr * 8) + i].u3 & CS_ATA)
                        tu_attn[ctlr] = 1;
@@ -533,7 +534,7 @@ tu_write(int ctlr, int unit, int reg, uint32 data) {
             if (tu_unit[(ctlr * 8) + i].u3 & CS_ATA)
                tu_attn[ctlr] = 1;
         }
-        clr_interrupt(tu_dib[ctlr].dev_num);
+        clr_interrupt(df10->devnum);
         if (((df10->status & IADR_ATTN) != 0 && tu_attn[ctlr] != 0) ||
              (df10->status & PI_ENABLE))
             df10_setirq(df10);