diff --git a/erlang/apps/as/src/assemble.erl b/erlang/apps/as/src/assemble.erl
index d6e7c53..73b2aff 100644
--- a/erlang/apps/as/src/assemble.erl
+++ b/erlang/apps/as/src/assemble.erl
@@ -106,11 +106,7 @@ insn_image(Insn, Tunit) ->
               ((case At of true -> 1; false -> 0 end) bsl (36 - 14)) bor
               ((Index band ((1 bsl 4) - 1)) bsl (36 - 18)) bor
               (Address band ((1 bsl 18) - 1))),
-      %% big-endian conversion
-      {ok, [(Word bsr 27) band 511,
-            (Word bsr 18) band 511,
-            (Word bsr  9) band 511,
-            Word          band 511]};
+      {ok, pdp10_extint:uint36_to_ext(Word)};
     {error, _Reason} = Error -> Error
   end.
 
diff --git a/erlang/apps/as/src/output.erl b/erlang/apps/as/src/output.erl
index 37c4197..31420a0 100644
--- a/erlang/apps/as/src/output.erl
+++ b/erlang/apps/as/src/output.erl
@@ -248,13 +248,10 @@ uint9_image(Uint9) ->
   Uint9 band 511.
 
 uint18_image(Uint18) ->
-  [(Uint18 bsr 9) band 511, Uint18 band 511].
+  pdp10_extint:uint18_to_ext(Uint18).
 
 uint36_image(Uint36) ->
-  [(Uint36 bsr 27) band 511,
-   (Uint36 bsr 18) band 511,
-   (Uint36 bsr  9) band 511,
-   Uint36          band 511].
+  pdp10_extint:uint36_to_ext(Uint36).
 
 image_size(Image) -> image_size(Image, 0).