diff --git a/tools/amalgamate.retro b/tools/amalgamate.retro
index ab73153..f8bdc81 100644
--- a/tools/amalgamate.retro
+++ b/tools/amalgamate.retro
@@ -26,6 +26,8 @@ Include compilation instructions and enable i/o devices.
   'CLOCK
   'SCRIPTING
 } [ '#define_ENABLE\_%s s:format s:put nl ] a:for-each nl
+
+'#define_BIT64 s:put nl
 ~~~
 
 Then extract and generate the single file source.