diff --git a/src/include/memory.h b/src/include/memory.h
index 4bf871d87..b274f73d2 100644
--- a/src/include/memory.h
+++ b/src/include/memory.h
@@ -1,6 +1,8 @@
 #ifndef _MEMORY_H
 #define _MEMORY_H
 
+#include <stddef.h>
+
 #ifndef HAVE_LIBGC
 extern void *tmalloc(size_t num);
 extern void *trealloc(void *str, size_t num);