diff --git a/doc/ref/posix.texi b/doc/ref/posix.texi
index 08d939b9f..5990322a4 100644
--- a/doc/ref/posix.texi
+++ b/doc/ref/posix.texi
@@ -1223,6 +1223,11 @@ valid separators.  Thus, programs should not assume that
 separator---e.g., when extracting the components of a file name.
 @end defvr
 
+@deffn {Scheme Procedure} in-vicinity @var{directory} @var{file}
+Concatenate @var{directory} and @var{file}, adding
+@code{file-name-separator-string} (by default slash) in between if it is
+not already present.  This helps create file names.
+@end deffn
 
 @node User Information
 @subsection User Information
diff --git a/module/ice-9/boot-9.scm b/module/ice-9/boot-9.scm
index 04f84215c..aaa998702 100644
--- a/module/ice-9/boot-9.scm
+++ b/module/ice-9/boot-9.scm
@@ -1,6 +1,6 @@
 ;;; -*- mode: scheme; coding: utf-8; -*-
 
-;;;; Copyright (C) 1995-2014, 2016-2024  Free Software Foundation, Inc.
+;;;; Copyright (C) 1995-2014, 2016-2025  Free Software Foundation, Inc.
 ;;;;
 ;;;; This library is free software; you can redistribute it and/or
 ;;;; modify it under the terms of the GNU Lesser General Public
@@ -2144,12 +2144,15 @@ non-locally, that exit determines the continuation."
                (file-name-separator-at-index? 2)
                (file-name-separator-at-index? 0)))))))
 
-(define (in-vicinity vicinity file)
-  (let ((tail (let ((len (string-length vicinity)))
+(define (in-vicinity directory file)
+  "Concatenate @var{directory} and @var{file}, adding
+@code{file-name-separator-string} (by default slash) in between if it is
+not already present.  This helps create file names."
+  (let ((tail (let ((len (string-length directory)))
                 (if (zero? len)
                     #f
-                    (string-ref vicinity (- len 1))))))
-    (string-append vicinity
+                    (string-ref directory (- len 1))))))
+    (string-append directory
                    (if (or (not tail) (file-name-separator? tail))
                        ""
                        file-name-separator-string)