diff --git a/lib/dns/include/dns/zt.h b/lib/dns/include/dns/zt.h
index 189092bc3b..2964fc971f 100644
--- a/lib/dns/include/dns/zt.h
+++ b/lib/dns/include/dns/zt.h
@@ -19,6 +19,7 @@
 #include <stdbool.h>
 
 #include <isc/lang.h>
+#include <isc/rwlock.h>
 
 #include <dns/types.h>