diff --git a/configure.ac b/configure.ac
index e2a5ae31..38c7b61d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -35,6 +35,9 @@ AM_MAINTAINER_MODE([enable])
 
 LT_INIT
 
+dnl Check for attributes
+AX_GCC_TYPE_ATTRIBUTE([transparent_union])
+
 dnl Checks for header files.
 AC_HEADER_ASSERT
 AC_HEADER_STDC
diff --git a/m4 b/m4
index 22e4bc9b..2d8eb252 160000
--- a/m4
+++ b/m4
@@ -1 +1 @@
-Subproject commit 22e4bc9b07982ced62289290e8d496b1c1a74853
+Subproject commit 2d8eb25218daa933d337df939b2427895b344344