diff --git a/src/stringpiece.h b/src/stringpiece.h
index 7299120..7ff826d 100644
--- a/src/stringpiece.h
+++ b/src/stringpiece.h
@@ -30,6 +30,7 @@
 
 #include <string.h>
 #include <algorithm>
+#include <cstddef>
 #include <iosfwd>
 #include <string>