diff --git a/res/res_resolver_unbound.c b/res/res_resolver_unbound.c
index 436a8ee359..a4e86a682e 100644
--- a/res/res_resolver_unbound.c
+++ b/res/res_resolver_unbound.c
@@ -25,6 +25,7 @@
 
 ASTERISK_REGISTER_FILE()
 
+#include <signal.h>
 #include <unbound.h>
 #include <arpa/nameser.h>