diff --git a/qse/doc/page/awk-lang.md b/qse/doc/page/awk-lang.md
index 13ac119d..de5200ca 100644
--- a/qse/doc/page/awk-lang.md
+++ b/qse/doc/page/awk-lang.md
@@ -1491,6 +1491,55 @@ BEGIN {
 }
 ~~~~~
 
+~~~~~{.awk}
+BEGIN {
+	if (sys::pipe(p0, p1, sys::O_NONBLOCK | sys::O_CLOEXEC) <= -1)
+	{
+		 print "pipe error";
+		 return -1;
+	}
+	a = sys::fork();
+	if (a <= -1)
+	{
+		print "fork error";
+		sys::close (p0);
+		sys::close (p1);
+	}
+	else if (a == 0)
+	{
+		## child
+		sys::close (p0);
+
+		stdout = sys::openfd(1);
+		sys::dup(p1, stdout);
+
+		print B"hello world";
+		print B"testing sys::dup()";
+		print B"writing to standard output..";
+
+		sys::close (p1);
+		sys::close (stdout);
+	}
+	else
+	{
+		sys::close (p1);
+		while (1)
+		{
+			n = sys::read(p0, k, 10);
+			if (n <= 0)
+			{
+				if (n == sys::RC_EAGAIN) continue; ## nonblock but data not available
+				if (n != 0) print "ERROR: " sys::errmsg();
+				break;
+			}
+			print "[" k "]";
+		}
+		sys::close (p0);
+		sys::wait(a);
+	}
+}
+~~~~~
+
 ~~~~~{.awk}
 BEGIN {
 	d = sys::opendir("/etc", sys::DIR_SORT);
diff --git a/qse/lib/awk/imap-imp.h b/qse/lib/awk/imap-imp.h
index 033fa6f7..be579ca9 100644
--- a/qse/lib/awk/imap-imp.h
+++ b/qse/lib/awk/imap-imp.h
@@ -61,16 +61,16 @@ static __IMAP_NODE_T* __MAKE_IMAP_NODE (qse_awk_rtx_t* rtx, __IMAP_LIST_T* list)
 
 	node = QSE_NULL;
 
-	if (list->free) node = list->free;
+	if (list->free) 
+	{
+		node = list->free;
+		list->free = node->next;
+	}
 	else
 	{
 		node = qse_awk_rtx_callocmem(rtx, QSE_SIZEOF(*node));
 		if (!node) goto oops;
-	}
-
-	if (node == list->free) list->free = node->next;
-	else
-	{
+		
 		if (list->map.high <= list->map.capa)
 		{
 			qse_size_t newcapa, inc;
@@ -92,11 +92,12 @@ static __IMAP_NODE_T* __MAKE_IMAP_NODE (qse_awk_rtx_t* rtx, __IMAP_LIST_T* list)
 		}
 
 		node->id = list->map.high;
-		QSE_ASSERT (list->map.tab[node->id] == QSE_NULL);
-		list->map.tab[node->id] = node;
 		list->map.high++;
 	}
 
+	QSE_ASSERT (list->map.tab[node->id] == QSE_NULL);
+	list->map.tab[node->id] = node;
+
 	/* append it to the tail */
 	node->next = QSE_NULL;
 	node->prev = list->tail;
diff --git a/qse/lib/awk/mod-str.c b/qse/lib/awk/mod-str.c
index 068454e5..58375551 100644
--- a/qse/lib/awk/mod-str.c
+++ b/qse/lib/awk/mod-str.c
@@ -30,6 +30,7 @@
 #include <qse/cmn/mbwc.h>
 #include "../cmn/mem-prv.h"
 #include "fnc.h"
+#include "val.h"
 
 static int fnc_normspace (qse_awk_rtx_t* rtx, const qse_awk_fnc_info_t* fi)
 {
diff --git a/qse/lib/awk/mod-sys.c b/qse/lib/awk/mod-sys.c
index a5327af2..c2cfb92e 100644
--- a/qse/lib/awk/mod-sys.c
+++ b/qse/lib/awk/mod-sys.c
@@ -484,7 +484,7 @@ static int fnc_openfd (qse_awk_rtx_t* rtx, const qse_awk_fnc_info_t* fi)
 		rx = awkerr_to_rc(qse_awk_rtx_geterrnum(rtx));
 		set_errmsg_on_sys_list (rtx, sys_list, QSE_NULL);
 	}
-	else if (fd >= 0)
+	else if (fd >= 0 && fd <= QSE_TYPE_MAX(int))
 	{
 		sys_node_t* sys_node;