diff -u a/src/kj/string-test.c++ b/src/kj/string-test.c++
--- a/src/kj/string-test.c++
+++ b/src/kj/string-test.c++
@@ -22,6 +22,7 @@
 #include "string.h"
 #include <kj/compat/gtest.h>
 #include <string>
+#include <cstdint>
 #include "vector.h"
 
 namespace kj {