diff --git a/require-ess/src/require.c b/require-ess/src/require.c
index 49200901bdf0a48963fdc522403e6eddb79cf573..b0c178bd4211f25c88bd7d42e7e4ce223eeb1f69 100644
--- a/require-ess/src/require.c
+++ b/require-ess/src/require.c
@@ -31,7 +31,6 @@
 #include <iocsh.h>
 #include <osiFileName.h>
 #include <recSup.h>
-#include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
diff --git a/require-ess/src/require.h b/require-ess/src/require.h
index f291d5767d5c7e81a2cd4f6bbc9f664f13653aee..e961d02df192e06d1e2e5297506570c40844f0a5 100644
--- a/require-ess/src/require.h
+++ b/require-ess/src/require.h
@@ -3,6 +3,8 @@
 
 #pragma once
 
+#include <stddef.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif  // __cplusplus