diff --git a/lib/isc/tests/ht_test.c b/lib/isc/tests/ht_test.c
index c8c8afad8c..618f29ea7e 100644
--- a/lib/isc/tests/ht_test.c
+++ b/lib/isc/tests/ht_test.c
@@ -23,6 +23,8 @@
 #include <isc/string.h>
 #include <isc/util.h>
 
+#include <inttypes.h>
+
 static void *
 default_memalloc(void *arg, size_t size) {
 	UNUSED(arg);