diff --git a/conf/Makefile.am b/conf/Makefile.am
index af604b594..8ce377daf 100644
--- a/conf/Makefile.am
+++ b/conf/Makefile.am
@@ -93,6 +93,8 @@ plugins_install_src = $(charon_plugins:%=plugins/%.conf)
 # has to be defined via autoconf as we can't do it with automake conditionals
 options_install_src = $(strongswan_options:%=options/%.conf)
 
+manparts = strongswan.conf.5.head strongswan.conf.5.main strongswan.conf.5.tail
+
 templates_DATA = strongswan.conf
 optionstemplate_DATA = $(options_install_src)
 pluginstemplate_DATA = $(plugins_install_src)
@@ -134,11 +136,12 @@ $(plugins_install_tmp):
 
 strongswan.conf.5.main: $(alloptions)
 	$(AM_V_GEN) \
-	$(PYTHON) $(srcdir)/format-options.py -f man $^ > $@
+	(cd $(srcdir) && \
+	 $(PYTHON) format-options.py -f man $(alloptions)) > $@
 
-strongswan.conf.5: strongswan.conf.5.head strongswan.conf.5.main strongswan.conf.5.tail
+strongswan.conf.5: $(manparts)
 	$(AM_V_GEN) \
-	cat $^ > $@
+	cat $(manparts) > $@
 
 clean-local:
 	rm -f plugins/*.conf plugins/*.tmp