diff --git a/lib/des/hash.h b/lib/des/hash.h
index 76b1b6f70..fb6976e8d 100644
--- a/lib/des/hash.h
+++ b/lib/des/hash.h
@@ -39,6 +39,7 @@
 
 #include <stdlib.h>
 #include <string.h>
+#include <stddef.h>
 #ifdef KRB5
 #include <krb5-types.h>
 #endif