diff --git a/m4/ax_gcc_builtin.m4 b/m4/ax_gcc_builtin.m4
index b28a91b..54d8729 100644
--- a/m4/ax_gcc_builtin.m4
+++ b/m4/ax_gcc_builtin.m4
@@ -24,6 +24,7 @@
 #   The macro currently supports the following built-in functions:
 #
 #    __builtin_assume_aligned
+#    __builtin_bswap16
 #    __builtin_bswap32
 #    __builtin_bswap64
 #    __builtin_choose_expr
@@ -90,7 +91,7 @@
 #   and this notice are preserved.  This file is offered as-is, without any
 #   warranty.
 
-#serial 2
+#serial 3
 
 AC_DEFUN([AX_GCC_BUILTIN], [
     AS_VAR_PUSHDEF([ac_var], [ax_cv_have_$1])
@@ -99,6 +100,7 @@ AC_DEFUN([AX_GCC_BUILTIN], [
         AC_LINK_IFELSE([AC_LANG_PROGRAM([], [
             m4_case([$1],
                 [__builtin_assume_aligned], [$1("", 0)],
+                [__builtin_bswap16], [$1(0)],
                 [__builtin_bswap32], [$1(0)],
                 [__builtin_bswap64], [$1(0)],
                 [__builtin_choose_expr], [$1(0, 0, 0)],