diff --git a/m4/ax_check_enable_debug.m4 b/m4/ax_check_enable_debug.m4
index 78adc3dee31122b0f680bd5295b21dcbe49877e1..c9e28db0ee5b2a1623280404f0776576cff7c780 100644
--- a/m4/ax_check_enable_debug.m4
+++ b/m4/ax_check_enable_debug.m4
@@ -117,8 +117,9 @@ AC_DEFUN([AX_CHECK_ENABLE_DEBUG],[
 
     dnl Define various variables if debugging is disabled.
     dnl assert.h is a NOP if NDEBUG is defined, so define it by default.
-    AS_IF([test "x$enable_debug" = "xyes"],
-      [m4_map_args_w(ax_enable_debug_vars, [AC_DEFINE(], [,,[Define if debugging is enabled])])],
-      [m4_map_args_w(ax_disable_debug_vars, [AC_DEFINE(], [,,[Define if debugging is disabled])])])
+    dnl XXX disabled as m4_map_args_w requires 2.64, and COSMA has 2.63.
+    dnl AS_IF([test "x$enable_debug" = "xyes"],
+    dnl  [m4_map_args_w(ax_enable_debug_vars, [AC_DEFINE(], [,,[Define if debugging is enabled])])],
+    dnl  [m4_map_args_w(ax_disable_debug_vars, [AC_DEFINE(], [,,[Define if debugging is disabled])])])
     ax_enable_debug=$enable_debug
 ])