diff --git a/src/grue.system.s b/src/grue.system.s
index b6d08c8..8121b32 100644
--- a/src/grue.system.s
+++ b/src/grue.system.s
@@ -5,6 +5,13 @@
 *=$2000
 !to "build/GRUE.SYSTEM",plain
 
+        lda     $BF98        ; machine identification byte
+        and     #$30
+        cmp     #$30         ; 128K?
+        bne     QuitToProDOS ; no, quit to ProDOS
+        !byte   $1a          ; 65C02 INC, clear Z flag if supported
+        beq     QuitToProDOS ; not a 65C02
+
 -       jsr     $bf00
 op_c7
         !byte   $c7
@@ -39,6 +46,13 @@ op_c7
         bne     -
         jmp     $1000
 
+QuitToProDOS
+        jsr     $bf00
+        !byte   $65
+        !word   quit_parms
+quit_parms
+        !byte   4
+
 c5_parms
         !byte   2
         !byte   0
diff --git a/src/pitchdark.a b/src/pitchdark.a
index 6c14a96..10c5a63 100644
--- a/src/pitchdark.a
+++ b/src/pitchdark.a
@@ -27,8 +27,10 @@ Start
          and   #$30
          cmp   #$30                  ; 128K?
          beq   +                     ; yes, continue
-         jmp   QuitToProDOS
-+        jsr   DisconnectRAM32       ; disconnect /RAM in S3,D2 so we can use DHGR
+-        jmp   QuitToProDOS
++        !byte $1a                   ; 65C02 INC, clear Z flag if supported
+         beq   -                     ; not a 65C02
+         jsr   DisconnectRAM32       ; disconnect /RAM in S3,D2 so we can use DHGR
          bit   $C010
          jsr   LoadFile              ; load WEEGUI binary at $4000
          !word .weeguiFilename