diff --git a/src/librustc/lint/builtin.rs b/src/librustc/lint/builtin.rs
index 109edffcde38..2bc31b00eb73 100644
--- a/src/librustc/lint/builtin.rs
+++ b/src/librustc/lint/builtin.rs
@@ -208,7 +208,7 @@ declare_lint! {
 
 declare_lint! {
     pub INCOHERENT_FUNDAMENTAL_IMPLS,
-    Warn,
+    Deny,
     "potentially-conflicting impls were erroneously allowed"
 }
 
diff --git a/src/test/compile-fail/issue-43355.rs b/src/test/compile-fail/issue-43355.rs
index 4db5c84df9a6..d793a78799a7 100644
--- a/src/test/compile-fail/issue-43355.rs
+++ b/src/test/compile-fail/issue-43355.rs
@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![deny(incoherent_fundamental_impls)]
-
 pub trait Trait1<X> {
     type Output;
 }
diff --git a/src/test/run-pass/issue-43355.rs b/src/test/run-pass/issue-43355.rs
deleted file mode 100644
index 19431a6a4292..000000000000
--- a/src/test/run-pass/issue-43355.rs
+++ /dev/null
@@ -1,36 +0,0 @@
-// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-// Check that the code for issue #43355 can run without an ICE, please remove
-// this test when it becomes an hard error.
-
-pub trait Trait1<X> {
-    type Output;
-}
-pub trait Trait2<X> {}
-
-impl<X, T> Trait1<X> for T where T: Trait2<X> {
-    type Output = ();
-}
-impl<X> Trait1<Box<X>> for A {
-    type Output = i32;
-}
-
-pub struct A;
-
-fn f<X, T: Trait1<Box<X>>>() {
-    println!("k: {}", ::std::mem::size_of::<<T as Trait1<Box<X>>>::Output>());
-}
-
-pub fn g<X, T: Trait2<Box<X>>>() {
-    f::<X, T>();
-}
-
-fn main() {}