diff --git a/lib/dns/include/dns/zt.h b/lib/dns/include/dns/zt.h
index 077b26ddea..037d0a9495 100644
--- a/lib/dns/include/dns/zt.h
+++ b/lib/dns/include/dns/zt.h
@@ -18,6 +18,7 @@
 #include <stdbool.h>
 
 #include <isc/lang.h>
+#include <isc/rwlock.h>
 
 #include <dns/types.h>