--- a/libguile/filesys.c	2016-11-05 15:03:52.131894648 +0100
+++ b/libguile/filesys.c	2016-11-05 15:07:13.275894481 +0100
@@ -791,24 +791,18 @@
 SCM_DEFINE (scm_mkdir, "mkdir", 1, 1, 0,
             (SCM path, SCM mode),
 	    "Create a new directory named by @var{path}.  If @var{mode} is omitted\n"
-	    "then the permissions of the directory file are set using the current\n"
-	    "umask.  Otherwise they are set to the decimal value specified with\n"
-	    "@var{mode}.  The return value is unspecified.")
+	    "then the permissions of the directory are set to @code{#o777}\n"
+	    "masked with the current umask (@pxref{Processes, @code{umask}}).\n"
+	    "Otherwise they are set to the value specified with @var{mode}.\n"
+	    "The return value is unspecified.")
 #define FUNC_NAME s_scm_mkdir
 {
   int rv;
-  mode_t mask;
+  mode_t c_mode;
 
-  if (SCM_UNBNDP (mode))
-    {
-      mask = umask (0);
-      umask (mask);
-      STRING_SYSCALL (path, c_path, rv = mkdir (c_path, 0777 ^ mask));
-    }
-  else
-    {
-      STRING_SYSCALL (path, c_path, rv = mkdir (c_path, scm_to_uint (mode)));
-    }
+  c_mode = SCM_UNBNDP (mode) ? 0777 : scm_to_uint (mode);
+
+  STRING_SYSCALL (path, c_path, rv = mkdir (c_path, c_mode));
   if (rv != 0)
     SCM_SYSERROR;
   return SCM_UNSPECIFIED;