diff --git a/build-aux/git-version-gen b/build-aux/git-version-gen
index 0fa90636..a8818b21 100755
--- a/build-aux/git-version-gen
+++ b/build-aux/git-version-gen
@@ -1,8 +1,8 @@
 #!/bin/sh
 # Print a version string.
-scriptversion=2012-03-18.17; # UTC
+scriptversion=2017-08-07.06; # UTC
 
-# Copyright (C) 2007-2012 Free Software Foundation, Inc.
+# Copyright (C) 2007-2017 Free Software Foundation, Inc.
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -85,7 +85,9 @@ Print a version string.
 
 Options:
 
-   --prefix           prefix of git tags (default 'v')
+   --prefix PREFIX    prefix of git tags (default 'v')
+   --fallback VERSION
+                      fallback version to use if \"git --version\" fails
 
    --help             display this help and exit
    --version          output version information and exit
@@ -93,20 +95,22 @@ Options:
 Running without arguments will suffice in most cases."
 
 prefix=v
+fallback=
 
 while test $# -gt 0; do
   case $1 in
     --help) echo "$usage"; exit 0;;
     --version) echo "$version"; exit 0;;
-    --prefix) shift; prefix="$1";;
+    --prefix) shift; prefix=${1?};;
+    --fallback) shift; fallback=${1?};;
     -*)
       echo "$0: Unknown option '$1'." >&2
       echo "$0: Try '--help' for more information." >&2
       exit 1;;
     *)
-      if test -z "$tarball_version_file"; then
+      if test "x$tarball_version_file" = x; then
         tarball_version_file="$1"
-      elif test -z "$tag_sed_script"; then
+      elif test "x$tag_sed_script" = x; then
         tag_sed_script="$1"
       else
         echo "$0: extra non-option argument '$1'." >&2
@@ -116,7 +120,7 @@ while test $# -gt 0; do
   shift
 done
 
-if test -z "$tarball_version_file"; then
+if test "x$tarball_version_file" = x; then
     echo "$usage"
     exit 1
 fi
@@ -140,11 +144,11 @@ then
         [0-9]*) ;;
         *) v= ;;
     esac
-    test -z "$v" \
+    test "x$v" = x \
         && echo "$0: WARNING: $tarball_version_file is missing or damaged" 1>&2
 fi
 
-if test -n "$v"
+if test "x$v" != x
 then
     : # use $v
 # Otherwise, if there is at least one git commit involving the working
@@ -163,9 +167,9 @@ then
     # tag or the previous older version that did not?
     #   Newer: v6.10-77-g0f8faeb
     #   Older: v6.10-g0f8faeb
-    case $v in
-        *-*-*) : git describe is okay three part flavor ;;
-        *-*)
+    case ${v#-g*} in
+        *-*) : git describe is probably okay three part flavor ;;
+        *)
             : git describe is older two part flavor
             # Recreate the number of commits and rewrite such that the
             # result is the same as if we were using the newer version
@@ -180,12 +184,14 @@ then
             ;;
     esac
 
-    # Change the first '-' to a '.', so version-comparing tools work properly.
-    # Remove the "g" in git describe's output string, to save a byte.
-    v=`echo "$v" | sed 's/-/./;s/\(.*\)-g/\1-/'`;
+    # Change the penultimate "-" to ".", for version-comparing tools.
+    # Remove the "g" to save a byte.
+    v=`echo "$v" | sed 's/-\([^-]*\)-g\([^-]*\)$/.\1-\2/'`;
     v_from_git=1
-else
+elif test "x$fallback" = x || git --version >/dev/null 2>&1; then
     v=UNKNOWN
+else
+    v=$fallback
 fi
 
 v=`echo "$v" |sed "s/^$prefix//"`
@@ -193,8 +199,8 @@ v=`echo "$v" |sed "s/^$prefix//"`
 # Test whether to append the "-dirty" suffix only if the version
 # string we're using came from git.  I.e., skip the test if it's "UNKNOWN"
 # or if it came from .tarball-version.
-if test -n "$v_from_git"; then
-  # Don't declare a version "dirty" merely because a time stamp has changed.
+if test "x$v_from_git" != x; then
+  # Don't declare a version "dirty" merely because a timestamp has changed.
   git update-index --refresh > /dev/null 2>&1
 
   dirty=`exec 2>/dev/null;git diff-index --name-only HEAD` || dirty=
@@ -209,12 +215,12 @@ if test -n "$v_from_git"; then
 fi
 
 # Omit the trailing newline, so that m4_esyscmd can use the result directly.
-echo "$v" | tr -d "$nl"
+printf %s "$v"
 
 # Local variables:
 # eval: (add-hook 'write-file-hooks 'time-stamp)
 # time-stamp-start: "scriptversion="
 # time-stamp-format: "%:y-%02m-%02d.%02H"
-# time-stamp-time-zone: "UTC"
+# time-stamp-time-zone: "UTC0"
 # time-stamp-end: "; # UTC"
 # End: