diff --git a/lib/memcoll.h b/lib/memcoll.h
index 4909bddff..b42cfa6f2 100644
--- a/lib/memcoll.h
+++ b/lib/memcoll.h
@@ -5,6 +5,8 @@
 #  include <config.h>
 # endif
 
+# include <stddef.h>
+
 # ifndef PARAMS
 #  if defined PROTOTYPES || (defined __STDC__ && __STDC__)
 #   define PARAMS(Args) Args