diff --git a/Makefile.legacy b/Makefile.legacy
index 0366fad..e26f0d2 100644
--- a/Makefile.legacy
+++ b/Makefile.legacy
@@ -69,10 +69,10 @@ genconf_parameters.sample: xpp/genconf_parameters
 README.html: README system.conf.asciidoc init.conf.asciidoc tonezones.txt \
   UPGRADE.txt genconf_parameters.asciidoc assigned-spans.conf.asciidoc \
   span-types.conf.asciidoc
-	$(ASCIIDOC) -n -a toc -a toclevels=4 $<
+	TZ=UTC $(ASCIIDOC) -n -a toc -a toclevels=4 $<
 
 README.Astribank.html: xpp/README.Astribank
-	$(ASCIIDOC) -o $@ -n -a toc -a toclevels=4 $<
+	TZ=UTC $(ASCIIDOC) -o $@ -n -a toc -a toclevels=4 $<
 
 # on Debian: this requires the full groff, not just groff-base.
 %.8.html: %.8