diff --git a/lib/chibi/filesystem.sld b/lib/chibi/filesystem.sld
index 09ccdda4..e00ab8cd 100644
--- a/lib/chibi/filesystem.sld
+++ b/lib/chibi/filesystem.sld
@@ -11,7 +11,7 @@
           close-file-descriptor renumber-file-descriptor
           delete-file link-file symbolic-link-file rename-file
           directory-files directory-fold create-directory delete-directory
-          open-pipe make-fifo
+          open open-pipe make-fifo
           file-status
           file-device               file-inode
           file-mode                 file-num-links
diff --git a/lib/chibi/filesystem.stub b/lib/chibi/filesystem.stub
index cb8475a8..c90ab69f 100644
--- a/lib/chibi/filesystem.stub
+++ b/lib/chibi/filesystem.stub
@@ -135,6 +135,10 @@
 
 (define-c errno (close-file-descriptor "close") (int))
 
+;;> Opens the given file and returns a file descriptor.
+
+(define-c int open (string int (default #o644 int)))
+
 ;;> Returns a list of 2 new file descriptors, the input and
 ;;> output end of a new pipe, respectively.