diff --git a/src/eckit/system/ResourceUsage.h b/src/eckit/system/ResourceUsage.h
index 98e847606..e9f961116 100644
--- a/src/eckit/system/ResourceUsage.h
+++ b/src/eckit/system/ResourceUsage.h
@@ -18,6 +18,7 @@
 #include <sys/resource.h>
 #include <cstddef>
 #include <iosfwd>
+#include <stddef.h>
 
 namespace eckit::system {