diff --git a/thun/asm-dump.txt b/thun/asm-dump.txt
index 3b4437a..7a60572 100644
--- a/thun/asm-dump.txt
+++ b/thun/asm-dump.txt
@@ -24,7 +24,7 @@ eq_offset(C),
 add(6, 6, 1),
 label(C),
 load_word(3, 5, 0),
-mov(1,6),
+mov(1, 6),
 asr_imm(6, 3, 30),
 and_imm(6, 6, 2),
 sub_imm(6, 6, 2),
@@ -50,7 +50,8 @@ label(G),
 store_word(2, 0, 0),
 do_offset(H),
 label(I),
-do_offset(I),label(J),
+do_offset(I),
+label(J),
 symbol(J),
 lsl_imm(6, 2, 2),
 asr_imm(6, 6, 17),
@@ -102,4 +103,4 @@ lsl_imm(5, 2, 2),
 asr_imm(5, 5, 17),
 do_offset(D),
 label(S),
-expr_cell(R, 0)].
\ No newline at end of file
+expr_cell(R, 0)].
diff --git a/thun/compiler.markII.pl b/thun/compiler.markII.pl
index 95a742c..77fffd0 100644
--- a/thun/compiler.markII.pl
+++ b/thun/compiler.markII.pl
@@ -109,12 +109,8 @@ Mark II
     chain_link(TOS, TEMP3),
     jump(Done),  % Rely on mainloop::Done to write TOS to RAM.
 
-    definition(Dup)
-]),[
-    % TermAddr := TOS << 2 >> 17
-    lsl_imm(TermAddr, TOS, 2),
-    asr_imm(TermAddr, TermAddr, 17)
-],⟐([
+    definition(Dup),
+    head_addr(TOS, TermAddr),
     jump(PUSH)
 ]),[
     label(Expression),
@@ -187,6 +183,8 @@ language.
 
 ⟐(definition(Name)) --> [label(Name), symbol(Name)].
 
+⟐(head_addr(Pair, HeadAddr)) --> [lsl_imm(HeadAddr, Pair, 2), asr_imm(HeadAddr, HeadAddr, 17)].
+
 
 do :-
     compile_program(Binary),