diff --git a/src/constraint-disabled.c b/src/constraint-disabled.c
index cf15256..5687fd7 100644
--- a/src/constraint-disabled.c
+++ b/src/constraint-disabled.c
@@ -36,6 +36,11 @@ constraint_check_child(void)
 {
 }
 
+void
+constraint_add(struct constraint *cstr)
+{
+}
+
 int
 constraint_dispatch_msg(struct pollfd *pfd)
 {