diff --git a/tool/generate_ech.cc b/tool/generate_ech.cc
index 1fe501d..f1e8cbe 100644
--- a/tool/generate_ech.cc
+++ b/tool/generate_ech.cc
@@ -14,6 +14,7 @@
 
 #include <stdio.h>
 
+#include <limits>
 #include <vector>
 
 #include <openssl/bytestring.h>