diff --git a/include/polarssl/base64.h b/include/polarssl/base64.h
index 2da935b..6610a18 100644
--- a/include/polarssl/base64.h
+++ b/include/polarssl/base64.h
@@ -24,7 +24,7 @@
 #ifndef POLARSSL_BASE64_H
 #define POLARSSL_BASE64_H
 
-#include <string.h>
+#include <stddef.h>
 
 #define POLARSSL_ERR_BASE64_BUFFER_TOO_SMALL               -0x002A  /**< Output buffer too small. */
 #define POLARSSL_ERR_BASE64_INVALID_CHARACTER              -0x002C  /**< Invalid character in input. */