https://svn.boost.org/trac/boost/ticket/10122

--- engine/mem.h
+++ engine/mem.h
@@ -8,6 +8,8 @@
 #ifndef BJAM_MEM_H
 #define BJAM_MEM_H
 
+#include "jam.h"
+
 #ifdef OPT_BOEHM_GC
 
     /* Use Boehm GC memory allocator. */