diff --git a/sorting/sort_recinfos.c b/sorting/sort_recinfos.c
index 6dbbb6efa83abef4d45b5e74d712f553d85f0faa..10e5a9902a6331bea8bd807d0b2c6bd10a03724b 100644
--- a/sorting/sort_recinfos.c
+++ b/sorting/sort_recinfos.c
@@ -1,6 +1,7 @@
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <inttypes.h>
 
 #include "config.h"
diff --git a/sorting/sort_records.c b/sorting/sort_records.c
index f44b6c142791f45e12fdaedadea344b0b014caf9..7127d851e2c401bc4b3ad159d9e66f06ec298df7 100644
--- a/sorting/sort_records.c
+++ b/sorting/sort_records.c
@@ -1,6 +1,7 @@
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <inttypes.h>
 
 #include "config.h"
diff --git a/sorting/sort_recptrs.c b/sorting/sort_recptrs.c
index 696752e76c9742efdd13e0dde2c13cdb59bbdc29..920394b297817089091c0979b9f63e09423aabf7 100644
--- a/sorting/sort_recptrs.c
+++ b/sorting/sort_recptrs.c
@@ -1,6 +1,7 @@
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <inttypes.h>
 
 #include "config.h"