diff --git a/xmpp-vala/src/module/xep/0115_entitiy_capabilities.vala b/xmpp-vala/src/module/xep/0115_entitiy_capabilities.vala
index 4f2dadfb..be7db509 100644
--- a/xmpp-vala/src/module/xep/0115_entitiy_capabilities.vala
+++ b/xmpp-vala/src/module/xep/0115_entitiy_capabilities.vala
@@ -147,7 +147,7 @@ namespace Xmpp.Xep.EntityCapabilities {
                     Gee.List<string> values = field.get_values();
                     values.sort();
                     foreach (string value in values) {
-                        sb.append(sanitize(value))
+                        sb.append(sanitize(value ?? ""))
                             .append("<");
                     }
                 }