diff --git a/lib/net_mosq.c b/lib/net_mosq.c
index 745b170..bdcaa19 100644
--- a/lib/net_mosq.c
+++ b/lib/net_mosq.c
@@ -50,6 +50,7 @@ Contributors:
 #include <openssl/conf.h>
 #include <openssl/engine.h>
 #include <openssl/err.h>
+#include <openssl/ui.h>
 #include <tls_mosq.h>
 #endif