configure.in should be named configure.ac these days

Makefile.in

@@ -38,7 +38,7 @@ SRCS = main.c screen.c client.c frame.c icc.c \
 		config_util.c launchermodule.c
 
 DISTFILES = README.md MODULES.md INSTALL LICENSE amiwm.1 \
-	configure configure.in Makefile.in install-sh smakefile scoptions \
+	configure configure.ac Makefile.in install-sh smakefile scoptions \
 	*.[chly] system.amiwmrc def_*.info *.map \
 	Background Background_resize Background_resize_norepeat \
 	Background_stretch Launcher Xresources.amiwm.in Amilogo.?m \
@@ -213,8 +213,8 @@ dist: version.h clean
 	  gzip $$tarname; \
 	)
 
-$(srcdir)/configure: $(srcdir)/configure.in
-	autoconf $(srcdir)/configure.in > $(srcdir)/configure
+$(srcdir)/configure: $(srcdir)/configure.ac
+	autoconf $(srcdir)/configure.ac > $(srcdir)/configure
 
 config.status: $(srcdir)/configure
 	$(srcdir)/configure