--- a/gnulib-tool
+++ b/gnulib-tool
@@ -4356,7 +4356,7 @@
     # PACKAGE is defined by AM_INIT_AUTOMAKE, PACKAGE_TARNAME is defined by AC_INIT.
     # See <http://lists.gnu.org/archive/html/automake/2009-05/msg00145.html>.
     echo "changequote(,)dnl"
-    echo "  ${macro_prefix}tests_WITNESS=IN_\`echo \"\${PACKAGE-\$PACKAGE_TARNAME}\" | LC_ALL=C tr 'a-z' 'A-Z' | LC_ALL=C sed -e 's/[^A-Z0-9_]/_/g'\`_GNULIB_TESTS"
+    echo "  ${macro_prefix}tests_WITNESS=IN_\`echo \"\${PACKAGE-\$PACKAGE_TARNAME}\" | LC_ALL=C tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ | LC_ALL=C sed -e 's/[^A-Z0-9_]/_/g'\`_GNULIB_TESTS"
     echo "changequote([, ])dnl"
     echo "  AC_SUBST([${macro_prefix}tests_WITNESS])"
     echo "  gl_module_indicator_condition=\$${macro_prefix}tests_WITNESS"