diff --git a/thun/compiler.markII.pl b/thun/compiler.markII.pl
index 9821a66..3f118d2 100644
--- a/thun/compiler.markII.pl
+++ b/thun/compiler.markII.pl
@@ -114,12 +114,12 @@ Mark II
 
     label(Cons)],  % Let's cons.
 
-    ⟐(unpack_pair(TOS, TEMP0, TOS)),
+    ⟐(unpack_pair(TOS, TEMP0, TOS, SP)),
     % TEMP0 = Address of the list to which to append.
     % TOS = Address of the second stack cell.
     [load_word(TEMP1, TOS, 0)],
     % TEMP1 contains the record of the second stack cell.
-    ⟐(unpack_pair(TEMP1, TEMP2, TEMP3)),
+    ⟐(unpack_pair(TEMP1, TEMP2, TEMP3, TOS)),
     % TEMP2 contains the address of the second item on the stack
     % TEMP3 = TOS +  TEMP1[15:0]  the address of the third stack cell
 
@@ -168,20 +168,20 @@ language.
      and_imm(Reg, Reg, 0x7fff),  % Mask off high bits.
      label(Label)].
 
-⟐(unpack_pair(From, HeadAddr, TailAddr)) -->
+⟐(unpack_pair(From, HeadAddr, TailAddr, Base)) -->
     [
     lsl_imm(HeadAddr, From, 2),  % Trim off the type tag 00 bits.
     asr_imm(HeadAddr, HeadAddr, 17),  % HeadAddr := From >> 15
     eq_offset(Label0),  % if the offset is zero don't add the address. it's empty list.
-    add(HeadAddr, HeadAddr, TOS),
+    add(HeadAddr, HeadAddr, Base),
     label(Label0),
     % HeadAddr contains the address of the second item on the stack
     lsl_imm(TailAddr, From, 17),  % Get the offset of the third stack cell
     asr_imm(TailAddr, TailAddr, 17),  % while preserving the sign.
     eq_offset(Label1),  % if the offset is zero don't add the address. it's empty list.
-    add(TailAddr, TailAddr, TOS),
+    add(TailAddr, TailAddr, Base),
     label(Label1)
-    % TailAddr = TOS +  From[15:0]  the address of the third stack cell
+    % TailAddr = Base +  From[15:0]  the address of the third stack cell
     ].