diff --git a/PDP11/pdp11_cpumod.c b/PDP11/pdp11_cpumod.c
index 9f7e80e00..8fc5e33aa 100644
--- a/PDP11/pdp11_cpumod.c
+++ b/PDP11/pdp11_cpumod.c
@@ -685,6 +685,9 @@ return SCPE_NXM;                                        /* unimplemented */
 t_stat CPU70_wr (int32 data, int32 pa, int32 access)
 {
 switch ((pa >> 1) & 017) {                              /* decode pa<4:1> */
+    case 000:
+    case 001:
+        return SCPE_OK;                                 /* error addr */
 
     case 002:                                           /* MEMERR */
         ODD_SHF (data);
@@ -708,6 +711,9 @@ switch ((pa >> 1) & 017) {                              /* decode pa<4:1> */
     case 011:                                           /* high size */
         return SCPE_OK;
 
+    case 012:                                           /* system ID */
+        return SCPE_OK;
+
     case 013:                                           /* CPUERR */
         CPUERR = 0;
         return SCPE_OK;