#define RUNAS_CHILD_STACK_SIZE 10485760
-#ifndef MAP_STACK
-#define MAP_STACK 0
+#ifndef __FreeBSD__
+# ifndef MAP_STACK
+# define MAP_STACK 0
+# endif
+#else /* FreeBSD MAP_STACK always return -ENOMEM */
+# define MAP_STACK 0
+#endif
+
+#ifndef MAP_GROWSDOWN
+#define MAP_GROWSDOWN 0
+#endif
+
+#ifndef MAP_ANONYMOUS
+#define MAP_ANONYMOUS MAP_ANON
#endif
struct run_as_data {