diff --git a/Makefile.docs b/Makefile.docs
index fe25d583e0..74650845b1 100644
--- a/Makefile.docs
+++ b/Makefile.docs
@@ -15,6 +15,8 @@ common_SPHINXOPTS =			\
 	-a				\
 	$(SPHINX_V)
 
+# The "today" variable set below is not directly used in the ARM, but its value
+# is implicitly inserted on the title page of the PDF file produced by Sphinx.
 ALLSPHINXOPTS =				\
 	$(common_SPHINXOPTS)		\
 	-D today="$(RELEASE_DATE)"	\
diff --git a/doc/arm/Makefile.am b/doc/arm/Makefile.am
index 5a13110956..915f19c42a 100644
--- a/doc/arm/Makefile.am
+++ b/doc/arm/Makefile.am
@@ -65,7 +65,7 @@ install-singlehtml: singlehtml
 	cp -R $(SPHINXBUILDDIR)/singlehtml/_static/* $(DESTDIR)/$(docdir)/_static/
 
 epub:
-	$(AM_V_SPHINX)$(SPHINX_BUILD) -b epub -A today=$(RELEASE_DATE) -d $(SPHINXBUILDDIR)/.doctrees/epub $(ALLSPHINXOPTS) $(SPHINXBUILDDIR)/epub
+	$(AM_V_SPHINX)$(SPHINX_BUILD) -b epub -d $(SPHINXBUILDDIR)/.doctrees/epub $(ALLSPHINXOPTS) $(SPHINXBUILDDIR)/epub
 
 install-epub:
 	$(INSTALL) -d $(DESTDIR)/$(docdir)