diff --git a/lib/dns/acl.c b/lib/dns/acl.c
index 8988fe95a2..a1b5680aae 100644
--- a/lib/dns/acl.c
+++ b/lib/dns/acl.c
@@ -17,6 +17,8 @@
 
 #include <config.h>
 
+#include <string.h>
+
 #include <isc/assertions.h>
 #include <isc/error.h>
 #include <isc/mem.h>