diff --git a/bitpack.h b/bitpack.h
index 049363f..cf8246b 100644
--- a/bitpack.h
+++ b/bitpack.h
@@ -29,6 +29,7 @@
 extern "C" {
 #endif
 #include <stdint.h>
+#include <stddef.h>
 
 //******************** Bit Packing High Level API - n unlimited ***************************************************
 size_t bitnpack8(     uint8_t  *__restrict in, size_t n, unsigned char *__restrict out); 
diff --git a/vp4.h b/vp4.h
index b867f95..17be982 100644
--- a/vp4.h
+++ b/vp4.h
@@ -29,6 +29,7 @@
 extern "C" {
 #endif
 #include <stdint.h>
+#include <stddef.h>
 //************************************************ High level API - n unlimited ****************************************************
 // Compress integer array with n values to the buffer out. 
 // Return value = number of bytes written to compressed buffer out