diff --git a/libexec/revnetgroup/parse_netgroup.c b/libexec/revnetgroup/parse_netgroup.c
index 13301df09fb..67e1b14788d 100644
--- a/libexec/revnetgroup/parse_netgroup.c
+++ b/libexec/revnetgroup/parse_netgroup.c
@@ -47,6 +47,7 @@ static const char rcsid[] =
  */
 
 #include <stdio.h>
+#include <string.h>
 #include <strings.h>
 #include <stdlib.h>
 #include <unistd.h>
diff --git a/usr.sbin/arp/arp.c b/usr.sbin/arp/arp.c
index 3c5866d65f4..9674f832661 100644
--- a/usr.sbin/arp/arp.c
+++ b/usr.sbin/arp/arp.c
@@ -78,6 +78,7 @@ static const char rcsid[] =
 #include <paths.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <strings.h>
 #include <unistd.h>
 
diff --git a/usr.sbin/fdformat/fdformat.c b/usr.sbin/fdformat/fdformat.c
index 0e037b4fec0..0e624dec270 100644
--- a/usr.sbin/fdformat/fdformat.c
+++ b/usr.sbin/fdformat/fdformat.c
@@ -37,6 +37,7 @@
 #include <paths.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <strings.h>
 #include <sysexits.h>
 #include <unistd.h>