diff --git a/include/llvm/Config/config.h.in b/include/llvm/Config/config.h.in
index 014380d7f83..765b3e100fe 100644
--- a/include/llvm/Config/config.h.in
+++ b/include/llvm/Config/config.h.in
@@ -164,6 +164,9 @@
 /* Define to 1 if you have the <unistd.h> header file. */
 #undef HAVE_UNISTD_H
 
+/* Define to 1 if the system has the type `u_int64_t'. */
+#undef HAVE_U_INT64_T
+
 /* Define to 1 if you have the <windows.h> header file. */
 #undef HAVE_WINDOWS_H