diff --git a/posix/Makefile b/posix/Makefile
index f9aa506..19c984e 100755
--- a/posix/Makefile
+++ b/posix/Makefile
@@ -1,5 +1,5 @@
 CFLAGS = $(WARNINGS) $(DEFINES) $(INCLUDES)
-DEFINES = $(DEBUG) -D_XOPEN_SOURCE=500 -DMISSING_POSIX_SPAWN
+DEFINES = $(DEBUG) -D_XOPEN_SOURCE=600 -DMISSING_POSIX_SPAWN -DMISSING_ENVIRON_DECL="extern char **environ"
 DEBUG= -D'debug(...)=fprintf(stderr,__VA_ARGS__)'
 # -D_POSIX_SOURCE -D_XOPEN_SOURCE=600 -D_POSIX_C_SOURCE=200112L \
 	-U__STRICT_ANSI__ -D_GNU_SOURCE
@@ -12,12 +12,10 @@ LIBS = -L$(LUA)/src -llua5.1
 
 ex-OBJS = ex.o spawn.o
 
-default: ex.dll
-
-ex.so: $(ex-OBJS); $(CC) -shared -o $@ $(ex-OBJS)
+default: ex.so
 
 EXTRA = posix_spawn.o
-ex.dll: $(ex-OBJS) $(EXTRA); $(CC) -shared -o $@ $(ex-OBJS) $(EXTRA) $(LIBS)
+ex.so: $(ex-OBJS) $(EXTRA); $(CC) -shared -o $@ $(ex-OBJS) $(EXTRA) $(LIBS)
 
 ex.o: ex.c spawn.h
 spawn.o: spawn.c spawn.h
diff --git a/posix/ex.c b/posix/ex.c
index dc9a6d9..9e8e6eb 100755
--- a/posix/ex.c
+++ b/posix/ex.c
@@ -3,6 +3,7 @@
 #include <ctype.h>
 #include <errno.h>
 #include <string.h>
+#include <unistd.h> /* environ */
 
 #include "lua.h"
 #include "lualib.h"
@@ -15,6 +16,8 @@
 
 #include "spawn.h"
 
+MISSING_ENVIRON_DECL;
+
 
 #define absindex(L,i) ((i)>0?(i):lua_gettop(L)+(i)+1)
 
@@ -384,12 +387,13 @@ static int ex_spawn(lua_State *L)
 		}
 		lua_getfield(L, 2, "env");              /* cmd opts ... envtab */
 		switch (lua_type(L, -1)) {
-		default: return luaL_error(L, "bad env option (table expected, got %s)",
-			luaL_typename(L, -1));
 		case LUA_TNIL:
+			break;
 		case LUA_TTABLE:
 			spawn_param_env(params);            /* cmd opts ... */
 			break;
+		default:
+			return luaL_error(L, "bad env option (table expected, got %s)", luaL_typename(L, -1));
 		}
 		get_redirect(L, 2, "stdin", params);    /* cmd opts ... */
 		get_redirect(L, 2, "stdout", params);   /* cmd opts ... */
diff --git a/posix/posix_spawn.c b/posix/posix_spawn.c
index cc69844..7514df4 100755
--- a/posix/posix_spawn.c
+++ b/posix/posix_spawn.c
@@ -8,6 +8,12 @@
 
 #include "posix_spawn.h"
 
+#ifndef OPEN_MAX
+#define OPEN_MAX sysconf(_SC_OPEN_MAX)
+#endif
+
+MISSING_ENVIRON_DECL;
+
 int posix_spawn_file_actions_init(posix_spawn_file_actions_t *act)
 {
 	act->dups[0] = act->dups[1] = act->dups[2] = -1;
@@ -16,10 +22,12 @@ int posix_spawn_file_actions_init(posix_spawn_file_actions_t *act)
 
 int posix_spawn_file_actions_adddup2(posix_spawn_file_actions_t *act, int d, int n)
 {
+	/* good faith effort to determine validity of descriptors */
 	if (d < 0 || OPEN_MAX < d || n < 0 || OPEN_MAX < n) {
 		errno = EBADF;
 		return -1;
 	}
+	/* we only support duplication to 0,1,2 */
 	if (2 < n) {
 		errno = EINVAL;
 		return -1;
diff --git a/posix/spawn.c b/posix/spawn.c
index 64b885f..fd30bdf 100755
--- a/posix/spawn.c
+++ b/posix/spawn.c
@@ -10,6 +10,7 @@
 #endif
 
 #include "spawn.h"
+MISSING_ENVIRON_DECL;
 
 struct spawn_params {
 	lua_State *L;
@@ -66,15 +67,11 @@ void spawn_param_args(struct spawn_params *p)
 	p->argv = argv;
 }
 
-/* ... envtab/nil */
+/* ... envtab */
 void spawn_param_env(struct spawn_params *p)
 {
 	size_t i = 0;
 	luaL_Buffer estr;
-	if (lua_isnil(p->L, -1)) {
-		p->envp = (const char **)environ;
-		return;
-	}
 	luaL_buffinit(p->L, &estr);
 	lua_newtable(p->L);                    /* ... envtab arr */
 	lua_pushnil(p->L);                     /* ... envtab arr nil */