diff --git a/res/res_resolver_unbound.c b/res/res_resolver_unbound.c
index 436a8ee359a29c6df11e18a6b61d7f77b68bda98..a4e86a682e63341ab3144dec4fb413a22ad01729 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>