--- ctags/configure.ac
+++ ctags/configure.ac
@@ -486,7 +486,7 @@ fi
 # -----------------------------
 AC_CHECKING(for new missing prototypes)
 
-AC_DEFUN(CHECK_PROTO, [
+AC_DEFUN([CHECK_PROTO], [
 	AC_EGREP_HEADER([[^A-Za-z0-9_]$1([ 	]+[A-Za-z0-9_]*)?[	 ]*\(],
 	$2,
 	,