diff --git a/src/bin/m4/lib/config.h b/src/bin/m4/lib/config.h
index 0c7b207796..431ef71f98 100644
--- a/src/bin/m4/lib/config.h
+++ b/src/bin/m4/lib/config.h
@@ -604,4 +604,4 @@
 /* #undef stack_t */
 
 /* Define as a macro for copying va_list variables. */
-/* #undef va_copy */
+#define va_copy gl_va_copy