diff --git a/lib/Plack/Builder.pm b/lib/Plack/Builder.pm
index 5156166d..9b4d44ee 100644
--- a/lib/Plack/Builder.pm
+++ b/lib/Plack/Builder.pm
@@ -109,9 +109,13 @@ sub builder(&) {
         $urlmap;
     };
     local $_add = sub {
+        defined wantarray
+            and Carp::carp("WARNING: You used enable() in non-void context");
         $self->add_middleware(@_);
     };
     local $_add_if = sub {
+        defined wantarray
+            and Carp::carp("WARNING: You used enable_if() in non-void context");
         $self->add_middleware_if(@_);
     };