diff --git a/lib/chibi/filesystem.stub b/lib/chibi/filesystem.stub
index cd4efaa2..2a4c8ddd 100644
--- a/lib/chibi/filesystem.stub
+++ b/lib/chibi/filesystem.stub
@@ -110,7 +110,7 @@
 ;;> Creates a new directory with the given mode.
 ;;> Returns \scheme{#t} on success and \scheme{#f} on failure.
 
-(define-c errno (create-directory "mkdir") (string int))
+(define-c errno (create-directory "mkdir") (string (default #o775 int)))
 
 ;;> Deletes the directory named \var{string} from the filesystem.
 ;;> Does not attempt to delete recursively.
@@ -149,7 +149,7 @@
 ;;> Creates a new named pipe in the given path.
 ;;> Returns \scheme{#t} on success and \scheme{#f} on failure.
 
-(define-c errno (make-fifo "mkfifo") (string (default #o644 int)))
+(define-c errno (make-fifo "mkfifo") (string (default #o664 int)))
 
 (define-c int (get-file-descriptor-flags "fcntl")
   (port-or-fileno (value F_GETFD int)))