diff --git a/src/Intrinsic.c b/src/Intrinsic.c
--- a/src/Intrinsic.c
+++ b/src/Intrinsic.c
@@ -1345,21 +1345,99 @@ FillInLangSubs(Substitution subs, XtPerDisplay pd)
 }
 
 /*
- * default path used if environment variable XFILESEARCHPATH
- * is not defined.  Also substitued for %D.
- * The exact value should be documented in the implementation
- * notes for any Xt implementation.
+   Return the default search path for the function
+   XtResolvePathname to use if XFILESEARCHPATH is
+   not defined.
+
+   It returns the combination the set of values which are the 6 "stems" below,
+   prepended with "/run/current-system/profile", and $GUIX_PROFILE and
+   "$HOME/.guix-profile"
+
+   These values provide the default paths where Guix/GuixSD can expect
+   to find resources for installed packages.
  */
 static const char *
-implementation_default_path(void)
+guix_default_path(void)
 {
-#if defined(WIN32)
-    static char xfilesearchpath[] = "";
+  static const char *search_path_default_stem[] = {
+    "/lib/X11/%L/%T/%N%C%S",
+    "/lib/X11/%l/%T/%N%C%S",
+    "/lib/X11/%T/%N%C%S",
+    "/lib/X11/%L/%T/%N%S",
+    "/lib/X11/%l/%T/%N%S",
+    "/lib/X11/%T/%N%S"
+  };
+
+#define SIZEOF_STEMS  (strlen (search_path_default_stem[0])	\
+		       + strlen (search_path_default_stem[1])	\
+		       + strlen (search_path_default_stem[2])	\
+		       + strlen (search_path_default_stem[3])	\
+		       + strlen (search_path_default_stem[4])	\
+		       + strlen (search_path_default_stem[5]))
+
+
+  int i;
+  const char *current_profile = "/run/current-system/profile";
+  char *home = getenv ("HOME");
+  char *guix_profile = getenv ("GUIX_PROFILE");
+
+  size_t bytesAllocd = SIZEOF_STEMS + 1;
+
+  /* This function is evaluated multiple times and the calling
+     code assumes that it is idempotent. So we must not allow
+     (say) a changed environment variable to cause it to return
+     something different. */
+  static char *path = NULL;
+  if (path)
+    return path;
+
+  bytesAllocd += 6 * (1 + strlen (current_profile));
+
+  if (guix_profile != NULL)
+    {
+      bytesAllocd += SIZEOF_STEMS;
+      bytesAllocd += 6 * (1 + strlen (guix_profile));
+    }
 
-    return xfilesearchpath;
-#else
-    return XFILESEARCHPATHDEFAULT;
-#endif
+  if (home != NULL)
+    {
+      bytesAllocd += SIZEOF_STEMS;
+      bytesAllocd += 6 * (1 + strlen(home) + strlen ("/.guix-profile"));
+    }
+
+  path = XtMalloc(bytesAllocd);
+  if (path == NULL) _XtAllocError(NULL);
+
+  memset (path, 0, bytesAllocd);
+
+  for (i = 0 ; i < 6 ; ++i)
+    {
+      strcat (path, current_profile);
+      strcat (path, search_path_default_stem[i]);
+      strcat (path, ":");
+    }
+
+  if (guix_profile != NULL)
+    for (i = 0 ; i < 6 ; ++i)
+      {
+	strcat (path, guix_profile);
+	strcat (path, search_path_default_stem[i]);
+	strcat (path, ":");
+      }
+
+  if (home != NULL)
+    for (i = 0 ; i < 6 ; ++i)
+      {
+	strcat (path, home);
+	strcat (path, "/.guix-profile");
+	strcat (path, search_path_default_stem[i]);
+	strcat (path, ":");
+      }
+
+  /* Remove final : */
+  path[strlen(path) - 1] = '\0';
+
+  return path;
 }
 
 
@@ -1388,7 +1466,7 @@ XtResolvePathname(Display *dpy,
 {
     XtPerDisplay pd;
     static const char *defaultPath = NULL;
-    const char *impl_default = implementation_default_path();
+    const char *impl_default = guix_default_path();
     int idef_len = (int) strlen(impl_default);
     char *massagedPath;
     int bytesAllocd, bytesLeft;
 normalize the FONT-FILE and IMAGE nested
variables.  Adjust doc.
* gnu/bootloader/depthcharge.scm (depthcharge-configuration-file): Adapt.
* gnu/bootloader/extlinux.scm (extlinux-configuration-file): Likewise.
* gnu/system/file-systems.scm (btrfs-subvolume?)
(btrfs-store-subvolume-file-name): New procedures.
* gnu/system.scm (operating-system-bootcfg): Specify the Btrfs
subvolume file name the store resides on to the
`operating-system-bootcfg' procedure, using the new
BTRFS-SUBVOLUME-FILE-NAME argument.
* doc/guix.texi (File Systems): Add a Btrfs subsection to document the use of
subvolumes.
* gnu/tests/install.scm (%btrfs-root-on-subvolume-os)
(%btrfs-root-on-subvolume-os-source)
(%btrfs-root-on-subvolume-installation-script)
(%test-btrfs-root-on-subvolume-os): New variables.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2020-01-03 16:06:26 +0100'>2020-01-03</span></td><td><a href='/guix/commit/gnu/bootloader/extlinux.scm?id=9512ba6b09b55c1551933c1885aa1ca39457aea8'>bootloader: Mark "grub.cfg" and "extlinux.conf" as non-substitutable.</a><span class='msg-avail'>...<span class='msg-tooltip'>Suggested by &lt;pkill9@runbox.com&gt;.

* gnu/bootloader/grub.scm (grub-configuration-file): Pass #:options to
'computed-file'.
* gnu/bootloader/extlinux.scm (extlinux-configuration-file): Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>