diff --git a/src/build/libroot/fs_descriptors.cpp b/src/build/libroot/fs_descriptors.cpp
index 2bf311dca6..68103e341c 100644
--- a/src/build/libroot/fs_descriptors.cpp
+++ b/src/build/libroot/fs_descriptors.cpp
@@ -1,3 +1,8 @@
+/*
+ * Copyright 2005-2011, Ingo Weinhold, ingo_weinhold@gmx.de.
+ * Distributed under the terms of the MIT License.
+ */
+
 
 #ifdef BUILDING_FS_SHELL
 #	include "compat.h"
@@ -507,4 +512,13 @@ delete_descriptor(int fd)
 	return error;
 }
 
+
+bool
+is_unknown_or_system_descriptor(int fd)
+{
+	Descriptor* descriptor = get_descriptor(fd);
+	return descriptor == NULL || descriptor->IsSystemFD();
+}
+
+
 } // namespace BPrivate
diff --git a/src/build/libroot/fs_descriptors.h b/src/build/libroot/fs_descriptors.h
index 608f6f6fc6..0df18381bb 100644
--- a/src/build/libroot/fs_descriptors.h
+++ b/src/build/libroot/fs_descriptors.h
@@ -1,3 +1,7 @@
+/*
+ * Copyright 2005-2011, Ingo Weinhold, ingo_weinhold@gmx.de.
+ * Distributed under the terms of the MIT License.
+ */
 #ifndef FS_DESCRIPTORS_H
 #define FS_DESCRIPTORS_H
 
@@ -118,6 +122,7 @@ struct AttrDirDescriptor : DirectoryDescriptor {
 Descriptor*	get_descriptor(int fd);
 int			add_descriptor(Descriptor *descriptor);
 status_t	delete_descriptor(int fd);
+bool		is_unknown_or_system_descriptor(int fd);
 
 }	// namespace BPrivate