diff --git a/src/core/cwuri.c b/src/core/cwuri.c
new file mode 100644
index 00000000..cf5e90f8
--- /dev/null
+++ b/src/core/cwuri.c
@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <stddef.h>
+#include <gpxe/uri.h>
+
+/** @file
+ *
+ * Current working URI
+ *
+ * Somewhat analogous to the current working directory in a POSIX
+ * system.
+ */
+
+/** Current working URI */
+struct uri *cwuri = NULL;
+
+/**
+ * Change working URI
+ *
+ * @v uri		New working URI
+ */
+void churi ( struct uri *uri ) {
+	if ( cwuri )
+		uri_put ( cwuri );
+	cwuri = uri_get ( uri );
+}
diff --git a/src/core/uri.c b/src/core/uri.c
index a793c457..8cb855a6 100644
--- a/src/core/uri.c
+++ b/src/core/uri.c
@@ -35,6 +35,8 @@
  * @v uri		URI
  */
 static void dump_uri ( struct uri *uri ) {
+	if ( ! uri )
+		return;
 	if ( uri->scheme )
 		DBG ( " scheme \"%s\"", uri->scheme );
 	if ( uri->opaque )
@@ -174,12 +176,14 @@ struct uri * parse_uri ( const char *uri_string ) {
 /**
  * Get port from URI
  *
- * @v uri		URI
+ * @v uri		URI, or NULL
  * @v default_port	Default port to use if none specified in URI
  * @ret port		Port
  */
 unsigned int uri_port ( struct uri *uri, unsigned int default_port ) {
-	return ( uri->port ? strtoul ( uri->port, NULL, 0 ) : default_port );
+	if ( ( ! uri ) || ( ! uri->port ) )
+		return default_port;
+	return ( strtoul ( uri->port, NULL, 0 ) );
 }
 
 /**
@@ -187,7 +191,7 @@ unsigned int uri_port ( struct uri *uri, unsigned int default_port ) {
  *
  * @v buf		Buffer to fill with URI string
  * @v size		Size of buffer
- * @v uri		URI to write into buffer
+ * @v uri		URI to write into buffer, or NULL
  * @ret len		Length of URI string
  */
 int unparse_uri ( char *buf, size_t size, struct uri *uri ) {
@@ -197,6 +201,13 @@ int unparse_uri ( char *buf, size_t size, struct uri *uri ) {
 	dump_uri ( uri );
 	DBG ( "\n" );
 
+	/* Special-case NULL URI */
+	if ( ! uri ) {
+		if ( size )
+			buf[0] = '\0';
+		return 0;
+	}
+
 	/* Special-case opaque URIs */
 	if ( uri->opaque ) {
 		return ssnprintf ( ( buf + used ), ( size - used ),
@@ -332,7 +343,7 @@ char * resolve_path ( const char *base_path,
 /**
  * Resolve base+relative URI
  *
- * @v base_uri		Base URI
+ * @v base_uri		Base URI, or NULL
  * @v relative_uri	Relative URI
  * @ret resolved_uri	Resolved URI
  *
@@ -347,7 +358,7 @@ struct uri * resolve_uri ( struct uri *base_uri,
 	struct uri *new_uri;
 
 	/* If relative URI is absolute, just re-use it */
-	if ( uri_is_absolute ( relative_uri ) )
+	if ( uri_is_absolute ( relative_uri ) || ( ! base_uri ) )
 		return uri_get ( relative_uri );
 
 	/* Mangle URI */
diff --git a/src/include/gpxe/uri.h b/src/include/gpxe/uri.h
index f6162382..b1389316 100644
--- a/src/include/gpxe/uri.h
+++ b/src/include/gpxe/uri.h
@@ -124,6 +124,8 @@ uri_put ( struct uri *uri ) {
 	ref_put ( &uri->refcnt );
 }
 
+extern struct uri *cwuri;
+
 extern struct uri * parse_uri ( const char *uri_string );
 extern unsigned int uri_port ( struct uri *uri, unsigned int default_port );
 extern int unparse_uri ( char *buf, size_t size, struct uri *uri );
@@ -132,5 +134,6 @@ extern char * resolve_path ( const char *base_path,
 			     const char *relative_path );
 extern struct uri * resolve_uri ( struct uri *base_uri,
 				  struct uri *relative_uri );
+extern void churi ( struct uri *uri );
 
 #endif /* _GPXE_URI_H */