diff --git a/disks/pc/unix/microport/system-v/2.3/README.md b/disks/pc/unix/microport/system-v/2.3/README.md
new file mode 100644
index 000000000..2257e41e9
--- /dev/null
+++ b/disks/pc/unix/microport/system-v/2.3/README.md
@@ -0,0 +1,36 @@
+Debugging Notes
+---
+
+The boot sector contains the following code:
+
+0000:7C3E B003            MOV      AL,03
+0000:7C40 B200            MOV      DL,00
+0000:7C42 B417            MOV      AH,17
+0000:7C44 CD13            INT      13
+0000:7C46 72B8            JC       7C00
+
+For BIOSes that don't support INT 0x13, AH function 0x17, patch the JC with two NOPs; eg:
+
+	e 0:7c46 90 90
+
+After booting, the following code is executed:
+
+12E8:01D3 52              PUSH     DX                   ;history=5
+12E8:01D4 51              PUSH     CX                   ;history=4
+12E8:01D5 2BC9            SUB      CX,CX                ;history=3
+12E8:01D7 BA6400          MOV      DX,0064              ;history=2
+12E8:01DA ED              IN       AX,DX                ;history=1
+
+For virtual machines that don't support word I/O to port 0x64, patch IN AX,DX with IN AL,DX; eg:
+
+	e 12e8:1da ec
+
+Here's where the first task switch (far jump using a TSS selector) occurs:
+
+	AX=02F0 BX=0008 CX=0000 DX=0000 SP=037E BP=037E SI=1852 DI=0000 
+    SS=0044[001800,07FF] DS=0228[009E00,851B] ES=0220[001000,8DFB] A20=ON 
+    CS=0200[012320,FFFD] LD=02E0[002000,01FF] GD=[001006,072F] ID=[0053E2,07FF] 
+    TR=02D0 MS=FFF5 PS=0016 V0 D0 I0 T0 S0 Z0 A1 P1 C0 
+    0200:016D FF6E06          JMP      FAR [BP+06]
+
+The far address at [BP+6] is 02F0:0000.
diff --git a/modules/pcjs/lib/x86seg.js b/modules/pcjs/lib/x86seg.js
index d17f0a545..bafe0cc7e 100644
--- a/modules/pcjs/lib/x86seg.js
+++ b/modules/pcjs/lib/x86seg.js
@@ -555,11 +555,10 @@ X86Seg.prototype.loadDesc8 = function(addrDesc, sel, fSuppress)
                 fGate = false;
             }
             else if (type == X86.DESC.ACC.TYPE.TSS) {
-                if (!this.switchTSS(sel, true)) {
+                if (!this.switchTSS(sel, fCall)) {
                     base = addrDesc = X86.ADDR_INVALID;
                     break;
                 }
-                if (DEBUG) cpu.stopCPU();
                 return this.base;
             }
             else if (type == X86.DESC.ACC.TYPE.GATE_CALL) {
@@ -581,7 +580,7 @@ X86Seg.prototype.loadDesc8 = function(addrDesc, sel, fSuppress)
                 cpu.assert(!(acc & 0x1f));
             }
             else if (type == X86.DESC.ACC.TYPE.GATE_TASK) {
-                if (!this.switchTSS(base & 0xffff, true)) {
+                if (!this.switchTSS(base & 0xffff, fCall)) {
                     base = addrDesc = X86.ADDR_INVALID;
                     break;
                 }
@@ -746,7 +745,7 @@ X86Seg.prototype.loadDesc8 = function(addrDesc, sel, fSuppress)
  *
  * @this {X86Seg}
  * @param {number} selNew
- * @param {boolean} fNest is true if nesting, false if un-nesting
+ * @param {boolean|null} [fNest] is true if nesting, false if un-nesting, null if neither
  * @return {boolean} true if successful, false if error
  */
 X86Seg.prototype.switchTSS = function switchTSS(selNew, fNest)
@@ -758,6 +757,9 @@ X86Seg.prototype.switchTSS = function switchTSS(selNew, fNest)
     var cplOld = this.cpl;
     var selOld = cpu.segTSS.sel;
     if (!fNest) {
+        /*
+         * TODO: Verify that it is (always) correct to require that the BUSY bit be currently set.
+         */
         if (cpu.segTSS.type != X86.DESC.ACC.TYPE.TSS_BUSY) {
             X86.fnFault.call(cpu, X86.EXCEPTION.TS_FAULT, selNew, true);
             return false;
@@ -771,7 +773,12 @@ X86Seg.prototype.switchTSS = function switchTSS(selNew, fNest)
     if (DEBUG && DEBUGGER && this.dbg && this.dbg.messageEnabled(Messages.TSS)) {
         this.dbg.message((fNest? "Task switch" : "Task return") + ": TR " + str.toHexWord(selOld) + " (%" + str.toHex(addrOld, 6) + "), new TR " + str.toHexWord(selNew) + " (%" + str.toHex(addrNew, 6) + ")");
     }
-    if (fNest) {
+    if (fNest === false) {
+        if (cpu.segTSS.type != X86.DESC.ACC.TYPE.TSS_BUSY) {
+            X86.fnFault.call(cpu, X86.EXCEPTION.GP_FAULT, selNew, true);
+            return false;
+        }
+    } else {
         if (cpu.segTSS.type == X86.DESC.ACC.TYPE.TSS_BUSY) {
             X86.fnFault.call(cpu, X86.EXCEPTION.GP_FAULT, selNew, true);
             return false;