--- jamvm-1.3.0/src/jam.h.orig	2005-04-02 14:38:49.000000000 +0200
+++ jamvm-1.3.0/src/jam.h	2005-04-02 14:41:18.000000000 +0200
@@ -531,13 +531,19 @@
 #define MIN_STACK 2*KB
 
 /* default minimum size of object heap */
+#ifndef DEFAULT_MIN_HEAP
 #define DEFAULT_MIN_HEAP 2*MB
+#endif
 
 /* default maximum size of object heap */
+#ifndef DEFAULT_MAX_HEAP
 #define DEFAULT_MAX_HEAP 128*MB
+#endif
 
 /* default size of the Java stack */
+#ifndef DEFAULT_STACK
 #define DEFAULT_STACK 64*KB
+#endif
 
 /* size of emergency area - big enough to create
    a StackOverflow exception */