diff --git a/docs/Makefile.am b/docs/Makefile.am
index e59b6c2..e1c76e2 100644
--- a/docs/Makefile.am
+++ b/docs/Makefile.am
@@ -108,7 +108,7 @@ $(HTML_DATA): build_stamp
 if ENABLE_DOCS
 
 reference/builddate.xml: $(REFERENCE_DEPS)
-	$(PYTHON) -c 'import datetime; print datetime.date.today()' > $@
+	$(PYTHON) -c 'import datetime, os, time; print datetime.datetime.utcfromtimestamp(int(os.environ.get("SOURCE_DATE_EPOCH", time.time()))).date()' > $@
 
 build_stamp: $(REFERENCE_DEPS)reference/builddate.xml
 	xsltproc --nonet --xinclude -o $(BUILDDIR)/html/ \