diff -Nurd yubico-c-libyubikey-1.13/Makefile.am yubico-c-libyubikey-1.13.new/Makefile.am
--- yubico-c-libyubikey-1.13/Makefile.am	2015-03-05 05:51:01.000000000 -0600
+++ yubico-c-libyubikey-1.13.new/Makefile.am	2018-08-01 08:40:22.590800618 -0500
@@ -68,7 +68,7 @@
 
 SUFFIXES = .1.txt .1
 .1.txt.1:
-	$(A2X) --format=manpage -a revdate="Version $(VERSION)" $<
+	$(A2X) -b manpage -a revdate="Version $(VERSION)" $<
 
 MANSOURCES = modhex.1.txt ykparse.1.txt ykgenerate.1.txt
 EXTRA_DIST = $(MANSOURCES) simple.mk THANKS