diff --git a/config.h.in b/config.h.in
index 53e0af8..ca29f91 100644
--- a/config.h.in
+++ b/config.h.in
@@ -6,6 +6,9 @@
 /* define if the compiler supports basic C++11 syntax */
 #undef HAVE_CXX11
 
+/* 1 if have memcmp in memory.h. */
+#undef HAVE_MEMCMP
+
 /* 1 if have memcpy in memory.h. */
 #undef HAVE_MEMCPY