diff --git a/bin/tests/system/dyndb/driver/db.c b/bin/tests/system/dyndb/driver/db.c
index ba247f6142..d9d4dd8121 100644
--- a/bin/tests/system/dyndb/driver/db.c
+++ b/bin/tests/system/dyndb/driver/db.c
@@ -12,6 +12,8 @@
  */
 #include <config.h>
 
+#include <isc/string.h>
+
 #include <dns/db.h>
 #include <dns/diff.h>
 #include <dns/enumclass.h>