diff --git a/build-aux/git-version-gen b/build-aux/git-version-gen
index fc727dd..ff0c534 100755
--- a/build-aux/git-version-gen
+++ b/build-aux/git-version-gen
@@ -2,8 +2,8 @@
 # Print a version string.
 scriptversion=2018-08-31.20; # UTC
 
-# Copyright (C) 2018 Red Hat, Inc.
-# Copyright (C) 2007-2010 Free Software Foundation, Inc.
+# Copyright (C) 2012-2020 Red Hat, Inc.
+# Copyright (C) 2007-2016 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
@@ -45,8 +45,10 @@ scriptversion=2018-08-31.20; # UTC
 #   files to pick up a version string change; and leave it stale to
 #   minimize rebuild time after unrelated changes to configure sources.
 #
-# It is probably wise to add these two files to .gitignore, so that you
-# don't accidentally commit either generated file.
+# As with any generated file in a VC'd directory, you should add
+# /.version to .gitignore, so that you don't accidentally commit it.
+# .tarball-version is never generated in a VC'd directory, so needn't
+# be listed there.
 #
 # In order to use git archive versions another two files has to be presented:
 #
@@ -69,58 +71,110 @@ scriptversion=2018-08-31.20; # UTC
 #         [bug-project@example])
 #
 # Then use the following lines in your Makefile.am, so that .version
-# will be present for dependencies, and so that .tarball-version will
-# exist in distribution tarballs.
+# will be present for dependencies, and so that .version and
+# .tarball-version will exist in distribution tarballs.
 #
+# EXTRA_DIST = $(top_srcdir)/.version
 # BUILT_SOURCES = $(top_srcdir)/.version
 # $(top_srcdir)/.version:
 #	echo $(VERSION) > $@-t && mv $@-t $@
 # dist-hook:
 #	echo $(VERSION) > $(distdir)/.tarball-version
 
-case $# in
-    1|2|3) ;;
-    *) echo 1>&2 "Usage: $0 \$srcdir/.tarball-version" \
-         '[$srcdir/.gitarchive-version] [TAG-NORMALIZATION-SED-SCRIPT]'
-       exit 1;;
-esac
 
-tarball_version_file=$1
-gitarchive_version_file=$2
-tag_sed_script="${3:-s/x/x/}"
+me=$0
+
+version="git-version-gen $scriptversion
+
+Copyright 2011 Free Software Foundation, Inc.
+There is NO warranty.  You may redistribute this software
+under the terms of the GNU General Public License.
+For more information about these matters, see the files named COPYING."
+
+usage="\
+Usage: $me [OPTION]... \$srcdir/.tarball-version [\$srcdir/.gitarchive-version] [TAG-NORMALIZATION-SED-SCRIPT]
+Print a version string.
+
+Options:
+
+   --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
+
+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";;
+    --fallback) shift; fallback="$1";;
+    -*)
+      echo "$0: Unknown option '$1'." >&2
+      echo "$0: Try '--help' for more information." >&2
+      exit 1;;
+    *)
+      if test "x$tarball_version_file" = x; then
+        tarball_version_file="$1"
+      elif test "x$gitarchive_version_file" = x; then
+        gitarchive_version_file="$1"
+      elif test "x$tag_sed_script" = x; then
+        tag_sed_script="$1"
+      else
+        echo "$0: extra non-option argument '$1'." >&2
+        exit 1
+      fi;;
+  esac
+  shift
+done
+
+if test "x$tarball_version_file" = x; then
+    echo "$usage"
+    exit 1
+fi
+
+tag_sed_script="${tag_sed_script:-s/x/x/}"
+
 nl='
 '
 
 # Avoid meddling by environment variable of the same name.
 v=
+v_from_git=
 
 # First see if there is a tarball-only version file.
 # then try "git describe", then default.
 if test -f $tarball_version_file
 then
-    v=`cat $tarball_version_file` || exit 1
+    v=`cat $tarball_version_file` || v=
     case $v in
-	*$nl*) v= ;; # reject multi-line output
-	[0-9]*) ;;
-	*) v= ;;
+        *$nl*) v= ;; # reject multi-line output
+        [0-9]*) ;;
+        *) v= ;;
     esac
-    test -z "$v" \
-	&& echo "$0: WARNING: $tarball_version_file seems to be damaged" 1>&2
+    test "x$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 $v
 # Otherwise, if there is at least one git commit involving the working
 # directory, and "git describe" output looks sensible, use that to
 # derive a version string.
 elif test "`git log -1 --pretty=format:x . 2>&1`" = x \
-    && v=`git describe --abbrev=4 --match='v*' HEAD 2>/dev/null \
-	  || git describe --abbrev=4 HEAD 2>/dev/null` \
+    && v=`git describe --abbrev=4 --match="$prefix*" HEAD 2>/dev/null \
+          || git describe --abbrev=4 HEAD 2>/dev/null` \
     && v=`printf '%s\n' "$v" | sed "$tag_sed_script"` \
     && case $v in
-	 v[0-9]*) ;;
-	 *) (exit 1) ;;
+         $prefix[0-9]*) ;;
+         *) (exit 1) ;;
        esac
 then
     # Is this a new git that lists number of commits since the last
@@ -128,39 +182,50 @@ then
     #   Newer: v6.10-77-g0f8faeb
     #   Older: v6.10-g0f8faeb
     case $v in
-	*-*-*) : git describe is okay three part flavor ;;
-	*-*)
-	    : git describe is older two part flavor
-	    # Recreate the number of commits and rewrite such that the
-	    # result is the same as if we were using the newer version
-	    # of git describe.
-	    vtag=`echo "$v" | sed 's/-.*//'`
-	    numcommits=`git rev-list "$vtag"..HEAD | wc -l`
-	    v=`echo "$v" | sed "s/\(.*\)-\(.*\)/\1-$numcommits-\2/"`;
-	    ;;
+        *-*-*) : git describe is okay three part flavor ;;
+        *-*)
+            : git describe is older two part flavor
+            # Recreate the number of commits and rewrite such that the
+            # result is the same as if we were using the newer version
+            # of git describe.
+            vtag=`echo "$v" | sed 's/-.*//'`
+            commit_list=`git rev-list "$vtag"..HEAD 2>/dev/null` \
+                || { commit_list=failed;
+                     echo "$0: WARNING: git rev-list failed" 1>&2; }
+            numcommits=`echo "$commit_list" | wc -l`
+            v=`echo "$v" | sed "s/\(.*\)-\(.*\)/\1-$numcommits-\2/"`;
+            test "$commit_list" = failed && v=UNKNOWN
+            ;;
     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-/'`;
-else
+    v_from_git=1
+elif test "x$fallback" = x || git --version >/dev/null 2>&1; then
     if test -f $gitarchive_version_file
     then
-        v=`sed 's/^.*tag: \(v[0-9][0-9]*\.[0-9][0-9]*\.[0-9][0-9]*\).*$/\1/' $gitarchive_version_file` || exit 1
+        v=`sed "s/^.*tag: \($prefix[0-9)][^,)]*\).*\$/\1/" $gitarchive_version_file \
+            | sed "$tag_sed_script"` || exit 1
         case $v in
             *$nl*) v= ;; # reject multi-line output
-            v[0-9]*) ;;
+            $prefix[0-9]*) ;;
             *) v= ;;
         esac
+
         test -z "$v" \
             && echo "$0: WARNING: $gitarchive_version_file doesn't contain valid version tag" 1>&2 \
             && v=UNKNOWN
-    else
+    elif test "x$fallback" = x; then
         v=UNKNOWN
+    else
+        v=$fallback
     fi
+else
+    v=$fallback
 fi
 
-if test "$v" = "UNKNOWN"
+if test "x$fallback" = x -a "$v" = "UNKNOWN"
 then
   echo "$0: ERROR: Can't find valid version. Please use valid git repository," \
     "released tarball or version tagged archive" 1>&2
@@ -168,28 +233,33 @@ then
   exit 1
 fi
 
-v=`echo "$v" |sed 's/^v//'`
+v=`echo "$v" |sed "s/^$prefix//"`
 
-# Don't declare a version "dirty" merely because a time stamp has changed.
-git update-index --refresh > /dev/null 2>&1
+# 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 "x$v_from_git" != x; then
+  # Don't declare a version "dirty" merely because a time stamp has changed.
+  git update-index --refresh > /dev/null 2>&1
 
-dirty=`sh -c 'git diff-index --name-only HEAD' 2>/dev/null` || dirty=
-case "$dirty" in
-    '') ;;
-    *) # Append the suffix only if there isn't one already.
-	case $v in
-	  *-dirty) ;;
-	  *) v="$v-dirty" ;;
-	esac ;;
-esac
+  dirty=`exec 2>/dev/null;git diff-index --name-only HEAD` || dirty=
+  case "$dirty" in
+      '') ;;
+      *) # Append the suffix only if there isn't one already.
+          case $v in
+            *-dirty) ;;
+            *) v="$v-dirty" ;;
+          esac ;;
+  esac
+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: