diff --git a/unpacktool/StringCommon.h b/unpacktool/StringCommon.h
index 38fcfab..5fc53c4 100644
--- a/unpacktool/StringCommon.h
+++ b/unpacktool/StringCommon.h
@@ -2,6 +2,7 @@
 
 #include <vector>
 #include <stdint.h>
+#include <stddef.h>
 
 namespace StringCommon
 {