diff --git a/lib/dns/ttl.c b/lib/dns/ttl.c
index d4bc04b097..5a4a28a849 100644
--- a/lib/dns/ttl.c
+++ b/lib/dns/ttl.c
@@ -19,6 +19,7 @@
 
 #include <ctype.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 
 #include <isc/assertions.h>