diff --git a/turbob64.h b/turbob64.h
index 0149b77..2ddd838 100644
--- a/turbob64.h
+++ b/turbob64.h
@@ -24,6 +24,9 @@
 // Turbo-Base64 - C/C++ include header
 #ifndef _TURBOB64_H_
 #define _TURBOB64_H_
+
+#include <stddef.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
