diff --git a/.gnulib b/.gnulib
index d6397dde2e..5b78831df0 160000
--- a/.gnulib
+++ b/.gnulib
@@ -1 +1 @@
-Subproject commit d6397dde2e127e246e3eeb5254a21f42cac783c8
+Subproject commit 5b78831df03b49408676227604cf16f90dee07ac
diff --git a/bootstrap b/bootstrap
index 92be11439a..ed3b0a4b70 100755
--- a/bootstrap
+++ b/bootstrap
@@ -1,6 +1,6 @@
 #! /bin/sh
 # Print a version string.
-scriptversion=2018-03-07.03; # UTC
+scriptversion=2018-07-01.02; # UTC
 
 # Bootstrap this package from checked-out sources.
 
@@ -47,6 +47,8 @@ PERL="${PERL-perl}"
 
 me=$0
 
+default_gnulib_url=git://git.sv.gnu.org/gnulib
+
 usage() {
   cat <<EOF
 Usage: $me [OPTION]...
@@ -76,6 +78,37 @@ contents are read as shell variables to configure the bootstrap.
 For build prerequisites, environment variables like \$AUTOCONF and \$AMTAR
 are honored.
 
+Gnulib sources can be fetched in various ways:
+
+ * If this package is in a git repository with a 'gnulib' submodule
+   configured, then that submodule is initialized and updated and sources
+   are fetched from there.  If \$GNULIB_SRCDIR is set (directly or via
+   --gnulib-srcdir) and is a git repository, then it is used as a reference.
+
+ * Otherwise, if \$GNULIB_SRCDIR is set (directly or via --gnulib-srcdir),
+   then sources are fetched from that local directory.  If it is a git
+   repository and \$GNULIB_REVISION is set, then that revision is checked
+   out.
+
+ * Otherwise, if this package is in a git repository with a 'gnulib'
+   submodule configured, then that submodule is initialized and updated and
+   sources are fetched from there.
+
+ * Otherwise, if the 'gnulib' directory does not exist, Gnulib sources are
+   cloned into that directory using git from \$GNULIB_URL, defaulting to
+   $default_gnulib_url.
+   If \$GNULIB_REVISION is set, then that revision is checked out.
+
+ * Otherwise, the existing Gnulib sources in the 'gnulib' directory are
+   used.  If it is a git repository and \$GNULIB_REVISION is set, then that
+   revision is checked out.
+
+If you maintain a package and want to pin a particular revision of the
+Gnulib sources that has been tested with your package, then there are two
+possible approaches: either configure a 'gnulib' submodule with the
+appropriate revision, or set \$GNULIB_REVISION (and if necessary
+\$GNULIB_URL) in $me.conf.
+
 Running without arguments will suffice in most cases.
 EOF
 }
@@ -109,9 +142,6 @@ die() { warn_ "$@"; exit 1; }
 
 # Configuration.
 
-# Name of the Makefile.am
-gnulib_mk=gnulib.mk
-
 # List of gnulib modules needed.
 gnulib_modules=
 
@@ -170,7 +200,15 @@ source_base=lib
 m4_base=m4
 doc_base=doc
 tests_base=tests
-gnulib_extra_files=''
+gnulib_extra_files="
+        build-aux/install-sh
+        build-aux/mdate-sh
+        build-aux/texinfo.tex
+        build-aux/depcomp
+        build-aux/config.guess
+        build-aux/config.sub
+        doc/INSTALL
+"
 
 # Additional gnulib-tool options to use.  Use "\newline" to break lines.
 gnulib_tool_option_extras=
@@ -264,24 +302,18 @@ case "$0" in
   *) test -r "$0.conf" && . ./"$0.conf" ;;
 esac
 
-# Extra files from gnulib, which override files from other sources.
-test -z "${gnulib_extra_files}" && \
-  gnulib_extra_files="
-        build-aux/install-sh
-        build-aux/mdate-sh
-        build-aux/texinfo.tex
-        build-aux/depcomp
-        build-aux/config.guess
-        build-aux/config.sub
-        doc/INSTALL
-"
-
 if test "$vc_ignore" = auto; then
   vc_ignore=
   test -d .git && vc_ignore=.gitignore
   test -d CVS && vc_ignore="$vc_ignore .cvsignore"
 fi
 
+if test x"$gnulib_modules$gnulib_files$gnulib_extra_files" = x; then
+  use_gnulib=false
+else
+  use_gnulib=true
+fi
+
 # Translate configuration into internal form.
 
 # Parse options.
@@ -612,85 +644,94 @@ git_modules_config () {
   test -f .gitmodules && git config --file .gitmodules "$@"
 }
 
-if $use_git; then
-  gnulib_path=$(git_modules_config submodule.gnulib.path)
-  test -z "$gnulib_path" && gnulib_path=gnulib
-fi
-
-# Get gnulib files.  Populate $GNULIB_SRCDIR, possibly updating a
-# submodule, for use in the rest of the script.
-
-case ${GNULIB_SRCDIR--} in
--)
-  # Note that $use_git is necessarily true in this case.
-  if git_modules_config submodule.gnulib.url >/dev/null; then
-    echo "$0: getting gnulib files..."
-    git submodule init -- "$gnulib_path" || exit $?
-    git submodule update -- "$gnulib_path" || exit $?
-
-  elif [ ! -d "$gnulib_path" ]; then
-    echo "$0: getting gnulib files..."
-
-    trap cleanup_gnulib 1 2 13 15
-
-    shallow=
-    git clone -h 2>&1 | grep -- --depth > /dev/null && shallow='--depth 2'
-    git clone $shallow git://git.sv.gnu.org/gnulib "$gnulib_path" ||
-      cleanup_gnulib
-
-    trap - 1 2 13 15
+if $use_gnulib; then
+  if $use_git; then
+    gnulib_path=$(git_modules_config submodule.gnulib.path)
+    test -z "$gnulib_path" && gnulib_path=gnulib
   fi
-  GNULIB_SRCDIR=$gnulib_path
-  ;;
-*)
-  # Use GNULIB_SRCDIR directly or as a reference.
-  if $use_git && test -d "$GNULIB_SRCDIR"/.git && \
-        git_modules_config submodule.gnulib.url >/dev/null; then
-    echo "$0: getting gnulib files..."
-    if git submodule -h|grep -- --reference > /dev/null; then
-      # Prefer the one-liner available in git 1.6.4 or newer.
-      git submodule update --init --reference "$GNULIB_SRCDIR" \
-        "$gnulib_path" || exit $?
-    else
-      # This fallback allows at least git 1.5.5.
-      if test -f "$gnulib_path"/gnulib-tool; then
-        # Since file already exists, assume submodule init already complete.
-        git submodule update -- "$gnulib_path" || exit $?
-      else
-        # Older git can't clone into an empty directory.
-        rmdir "$gnulib_path" 2>/dev/null
-        git clone --reference "$GNULIB_SRCDIR" \
-          "$(git_modules_config submodule.gnulib.url)" "$gnulib_path" \
-          && git submodule init -- "$gnulib_path" \
-          && git submodule update -- "$gnulib_path" \
-          || exit $?
+
+  # Get gnulib files.  Populate $GNULIB_SRCDIR, possibly updating a
+  # submodule, for use in the rest of the script.
+
+  case ${GNULIB_SRCDIR--} in
+  -)
+    # Note that $use_git is necessarily true in this case.
+    if git_modules_config submodule.gnulib.url >/dev/null; then
+      echo "$0: getting gnulib files..."
+      git submodule init -- "$gnulib_path" || exit $?
+      git submodule update -- "$gnulib_path" || exit $?
+
+    elif [ ! -d "$gnulib_path" ]; then
+      echo "$0: getting gnulib files..."
+
+      trap cleanup_gnulib 1 2 13 15
+
+      shallow=
+      if test -z "$GNULIB_REVISION"; then
+        git clone -h 2>&1 | grep -- --depth > /dev/null && shallow='--depth 2'
       fi
+      git clone $shallow ${GNULIB_URL:-$default_gnulib_url} "$gnulib_path" \
+        || cleanup_gnulib
+
+      trap - 1 2 13 15
     fi
     GNULIB_SRCDIR=$gnulib_path
+    ;;
+  *)
+    # Use GNULIB_SRCDIR directly or as a reference.
+    if $use_git && test -d "$GNULIB_SRCDIR"/.git && \
+          git_modules_config submodule.gnulib.url >/dev/null; then
+      echo "$0: getting gnulib files..."
+      if git submodule -h|grep -- --reference > /dev/null; then
+        # Prefer the one-liner available in git 1.6.4 or newer.
+        git submodule update --init --reference "$GNULIB_SRCDIR" \
+          "$gnulib_path" || exit $?
+      else
+        # This fallback allows at least git 1.5.5.
+        if test -f "$gnulib_path"/gnulib-tool; then
+          # Since file already exists, assume submodule init already complete.
+          git submodule update -- "$gnulib_path" || exit $?
+        else
+          # Older git can't clone into an empty directory.
+          rmdir "$gnulib_path" 2>/dev/null
+          git clone --reference "$GNULIB_SRCDIR" \
+            "$(git_modules_config submodule.gnulib.url)" "$gnulib_path" \
+            && git submodule init -- "$gnulib_path" \
+            && git submodule update -- "$gnulib_path" \
+            || exit $?
+        fi
+      fi
+      GNULIB_SRCDIR=$gnulib_path
+    fi
+    ;;
+  esac
+
+  if test -d "$GNULIB_SRCDIR"/.git && test -n "$GNULIB_REVISION" \
+     && ! git_modules_config submodule.gnulib.url >/dev/null; then
+    (cd "$GNULIB_SRCDIR" && git checkout "$GNULIB_REVISION") || cleanup_gnulib
   fi
-  ;;
-esac
 
-# $GNULIB_SRCDIR now points to the version of gnulib to use, and
-# we no longer need to use git or $gnulib_path below here.
+  # $GNULIB_SRCDIR now points to the version of gnulib to use, and
+  # we no longer need to use git or $gnulib_path below here.
 
-if $bootstrap_sync; then
-  cmp -s "$0" "$GNULIB_SRCDIR/build-aux/bootstrap" || {
-    echo "$0: updating bootstrap and restarting..."
-    case $(sh -c 'echo "$1"' -- a) in
-      a) ignored=--;;
-      *) ignored=ignored;;
-    esac
-    exec sh -c \
-      'cp "$1" "$2" && shift && exec "${CONFIG_SHELL-/bin/sh}" "$@"' \
-      $ignored "$GNULIB_SRCDIR/build-aux/bootstrap" \
-      "$0" "$@" --no-bootstrap-sync
-  }
+  if $bootstrap_sync; then
+    cmp -s "$0" "$GNULIB_SRCDIR/build-aux/bootstrap" || {
+      echo "$0: updating bootstrap and restarting..."
+      case $(sh -c 'echo "$1"' -- a) in
+        a) ignored=--;;
+        *) ignored=ignored;;
+      esac
+      exec sh -c \
+        'cp "$1" "$2" && shift && exec "${CONFIG_SHELL-/bin/sh}" "$@"' \
+        $ignored "$GNULIB_SRCDIR/build-aux/bootstrap" \
+        "$0" "$@" --no-bootstrap-sync
+    }
+  fi
+
+  gnulib_tool=$GNULIB_SRCDIR/gnulib-tool
+  <$gnulib_tool || exit $?
 fi
 
-gnulib_tool=$GNULIB_SRCDIR/gnulib-tool
-<$gnulib_tool || exit $?
-
 # Get translations.
 
 download_po_files() {
@@ -898,32 +939,33 @@ fi
 
 # Import from gnulib.
 
-gnulib_tool_options="\
- --import\
- --no-changelog\
- --aux-dir $build_aux\
- --doc-base $doc_base\
- --lib $gnulib_name\
- --m4-base $m4_base/\
- --source-base $source_base/\
- --tests-base $tests_base\
- --local-dir $local_gl_dir\
- $gnulib_tool_option_extras\
-"
-if test $use_libtool = 1; then
-  case "$gnulib_tool_options " in
-    *' --libtool '*) ;;
-    *) gnulib_tool_options="$gnulib_tool_options --libtool" ;;
-  esac
-fi
-echo "$0: $gnulib_tool $gnulib_tool_options --import ..."
-$gnulib_tool $gnulib_tool_options --import $gnulib_modules \
-  || die "gnulib-tool failed"
+if $use_gnulib; then
+  gnulib_tool_options="\
+   --no-changelog\
+   --aux-dir=$build_aux\
+   --doc-base=$doc_base\
+   --lib=$gnulib_name\
+   --m4-base=$m4_base/\
+   --source-base=$source_base/\
+   --tests-base=$tests_base\
+   --local-dir=$local_gl_dir\
+   $gnulib_tool_option_extras\
+  "
+  if test $use_libtool = 1; then
+    case "$gnulib_tool_options " in
+      *' --libtool '*) ;;
+      *) gnulib_tool_options="$gnulib_tool_options --libtool" ;;
+    esac
+  fi
+  echo "$0: $gnulib_tool $gnulib_tool_options --import ..."
+  $gnulib_tool $gnulib_tool_options --import $gnulib_modules \
+    || die "gnulib-tool failed"
 
-for file in $gnulib_files; do
-  symlink_to_dir "$GNULIB_SRCDIR" $file \
-    || die "failed to symlink $file"
-done
+  for file in $gnulib_files; do
+    symlink_to_dir "$GNULIB_SRCDIR" $file \
+      || die "failed to symlink $file"
+  done
+fi
 
 bootstrap_post_import_hook \
   || die "bootstrap_post_import_hook failed"