diff --git a/core/lib/src/response/responder.rs b/core/lib/src/response/responder.rs
index 5e6937e5..1e33d4de 100644
--- a/core/lib/src/response/responder.rs
+++ b/core/lib/src/response/responder.rs
@@ -271,10 +271,17 @@ impl<'r, R: Responder<'r>> Responder<'r> for Option<R> {
 /// If `self` is `Ok`, responds with the wrapped `Responder`. Otherwise prints
 /// an error message with the `Err` value returns an `Err` of
 /// `Status::InternalServerError`.
+#[deprecated(since = "0.4.3")]
 impl<'r, R: Responder<'r>, E: fmt::Debug> Responder<'r> for Result<R, E> {
     default fn respond_to(self, req: &Request) -> response::Result<'r> {
         self.map(|r| r.respond_to(req)).unwrap_or_else(|e| {
             error_!("Response was a non-`Responder` `Err`: {:?}.", e);
+            warn_!("This `Responder` implementation has been deprecated.");
+            warn_!(
+                "In Rocket v0.5, `Result<T, E>` implements `Responder` only if \
+                `E` implements `Responder`. For the previous behavior, use \
+                `Result<T, Debug<E>>` where `Debug` is `rocket::response::Debug`."
+            );
             Err(Status::InternalServerError)
         })
     }