diff --git a/configure.in b/configure.in
index 880c1680..0572e7d7 100644
--- a/configure.in
+++ b/configure.in
@@ -1410,7 +1410,16 @@ AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <stddef.h>
 
 if test "$cf_result" = "yes"; then
 	AC_DEFINE([HAVE_ALLOCA])
-	AC_DEFINE([_ALLOCA_H], [1], [alloca of tcc])
+	AC_DEFINE([_ALLOCA_H], [1], [Define as 1 if you are using Tiny C Compiler
+		with the GNU C Library,	and <alloca.h> of glibc would otherwise
+		override the alloca macro defined in <stddef.h> of TCC.
+		If <alloca.h> of glibc sees the _ALLOCA_H macro, it assumes
+		it has already been included, and does not redefine alloca.
+		This might not work in future glibc versions though, because
+		the names of the #include guard macros are not documented.
+		The incompatibility has been reported to the tinycc-devel
+		mailing list on 2008-07-14.  If a future version of TCC provides
+		an <alloca.h> of its own, this hack won't be needed.])
 fi
 # ===================================================================
 # A little fine tuning of gcc specific options (continued)