diff --git a/SDS/sds_cpu.c b/SDS/sds_cpu.c
index 70dc2429..9fda030c 100644
--- a/SDS/sds_cpu.c
+++ b/SDS/sds_cpu.c
@@ -428,9 +428,31 @@ while (reason == 0) {                                   /* loop until halted */
         int_reqhi = api_findreq ();                     /* recalc int req */
         }
     else {                                              /* normal instr */
-        if (sim_brk_summ && sim_brk_test (P, SWMASK ('E'))) { /* breakpoint? */
-            reason = STOP_IBKPT;                        /* stop simulation */
-            break;
+        if (sim_brk_summ) {
+            uint32 btyp = SWMASK ('E');
+
+            if (nml_mode)
+                btyp = SWMASK ('E') | SWMASK ('N');
+            else
+                btyp = usr_mode ? SWMASK ('E') | SWMASK ('U')
+                                : SWMASK ('E') | SWMASK ('M');
+            btyp = sim_brk_test (P, btyp); 
+            if (btyp) {
+                if (btyp & SWMASK ('E'))                /* unqualified breakpoint? */
+                    reason = STOP_IBKPT;                /* stop simulation */
+                else switch (btyp) {                    /* qualified breakpoint */
+                    case SWMASK ('M'):                  /* monitor mode */
+                        reason = STOP_MBKPT;            /* stop simulation */
+                        break;
+                    case SWMASK ('N'):                  /* normal (SDS 930) mode */
+                        reason = STOP_NBKPT;            /* stop simulation */
+                        break;
+                    case SWMASK ('U'):                  /* user mode */
+                        reason = STOP_UBKPT;            /* stop simulation */
+                        break;
+                    }
+                break;
+                }
             }
         reason = Read (save_P = P, &inst);              /* get instr */
         P = (P + 1) & VA_MASK;                          /* incr PC */
@@ -1473,7 +1495,8 @@ pcq_r = find_reg ("PCQ", NULL, dptr);
 if (pcq_r)
     pcq_r->qptr = 0;
 else return SCPE_IERR;
-sim_brk_types = sim_brk_dflt = SWMASK ('E');
+sim_brk_dflt = SWMASK ('E');
+sim_brk_types = SWMASK ('E') | SWMASK ('M') | SWMASK ('N') | SWMASK ('U');
 return SCPE_OK;
 }
 
diff --git a/SDS/sds_defs.h b/SDS/sds_defs.h
index 8277a144..82955c8b 100644
--- a/SDS/sds_defs.h
+++ b/SDS/sds_defs.h
@@ -1,4 +1,4 @@
-/* sds_defs.h: SDS 940 simulator definitions 
+/* sds_defs.h: SDS 940 simulator definitions
 
    Copyright (c) 2001-2010, Robert M. Supnik
 
@@ -52,6 +52,9 @@
 #define STOP_RTCINS     12                              /* rtc inst not MIN/SKR */
 #define STOP_ILLVEC     13                              /* zero vector */
 #define STOP_CCT        14                              /* runaway CCT */
+#define STOP_MBKPT      15                              /* monitor-mode breakpoint */
+#define STOP_NBKPT      16                              /* normal-mode breakpoint */
+#define STOP_UBKPT      17                              /* user-mode breakpoint */
 
 /* Trap codes */
 
diff --git a/SDS/sds_sys.c b/SDS/sds_sys.c
index 964975b7..14a03c82 100644
--- a/SDS/sds_sys.c
+++ b/SDS/sds_sys.c
@@ -96,7 +96,10 @@ const char *sim_stop_messages[] = {
     "Trap instruction not BRM",
     "RTC instruction not MIN or SKR",
     "Interrupt vector zero",
-    "Runaway carriage control tape"
+    "Runaway carriage control tape",
+    "Monitor-mode Breakpoint",
+    "Normal-mode Breakpoint",
+    "User-mode Breakpoint"
     };
 
 /* Character conversion tables */