diff --git a/core/vip.c b/core/vip.c
index 0860890..74b9bb2 100644
--- a/core/vip.c
+++ b/core/vip.c
@@ -481,10 +481,12 @@ static void vipWriteIO(
             break;
 
         case 0x5F830>>1: /* CTA */
-            if ((mask & 0xFF00) == 0)
-                sim->vip.cta.cta_r = value >> 8;
-            if ((mask & 0x00FF) == 0)
-                sim->vip.cta.cta_l = value;
+            if (debug) {
+                if ((mask & 0xFF00) == 0)
+                    sim->vip.cta.cta_r = value >> 8;
+                if ((mask & 0x00FF) == 0)
+                    sim->vip.cta.cta_l = value;
+            }
             break;
 
         case 0x5F842>>1: /* XPCTRL */
diff --git a/util/disassembler.c b/util/disassembler.c
index 2f1a596..896f34c 100644
--- a/util/disassembler.c
+++ b/util/disassembler.c
@@ -513,6 +513,8 @@ static int dasmLine(VB *sim, uint32_t *address, uint32_t pc,
     line->isPC       = *address == pc;
     for (x = 0; x < line->codeLength; x++)
         line->code[x] = vbRead(sim, *address + x, VB_U8);
+
+    /* Advance to the next instruction or PC, whichever is sooner */
     *address += pc != *address && pc - *address < line->codeLength ?
         pc - *address : line->codeLength;
 
@@ -657,6 +659,8 @@ static VBU_DasmLine* dasmDisassemble(VB *sim, uint32_t address,
         size = vbuCodeSize(sim, addr);
         if (address - addr < size)
             break;
+
+        /* Advance to the next instruction or PC, whichever is sooner */
         addr += addr != pc && pc - addr < size ? pc - addr : size;
     }