diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index a49926158de..8a066f3f4a0 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -563,6 +563,7 @@ declare_features! (
 // unanticipated results, such as compiler crashes. We warn the user about these
 // to alert them.
 const INCOMPLETE_FEATURES: &[Symbol] = &[
+    sym::impl_trait_in_bindings,
     sym::generic_associated_types,
     sym::const_generics
 ];
diff --git a/src/test/run-pass/impl-trait-in-bindings.rs b/src/test/run-pass/impl-trait-in-bindings.rs
index 9a1f53b4893..1e3a641b7cf 100644
--- a/src/test/run-pass/impl-trait-in-bindings.rs
+++ b/src/test/run-pass/impl-trait-in-bindings.rs
@@ -1,4 +1,5 @@
 #![feature(impl_trait_in_bindings)]
+//~^ WARN the feature `impl_trait_in_bindings` is incomplete and may cause the compiler to crash
 
 use std::fmt::Debug;
 
diff --git a/src/test/run-pass/impl-trait-in-bindings.stderr b/src/test/run-pass/impl-trait-in-bindings.stderr
new file mode 100644
index 00000000000..4896deb9d5c
--- /dev/null
+++ b/src/test/run-pass/impl-trait-in-bindings.stderr
@@ -0,0 +1,6 @@
+warning: the feature `impl_trait_in_bindings` is incomplete and may cause the compiler to crash
+  --> $DIR/impl-trait-in-bindings.rs:1:12
+   |
+LL | #![feature(impl_trait_in_bindings)]
+   |            ^^^^^^^^^^^^^^^^^^^^^^
+
diff --git a/src/test/ui/impl-trait/bindings-opaque.rs b/src/test/ui/impl-trait/bindings-opaque.rs
index 5f623321943..d4eef29ed32 100644
--- a/src/test/ui/impl-trait/bindings-opaque.rs
+++ b/src/test/ui/impl-trait/bindings-opaque.rs
@@ -1,4 +1,5 @@
 #![feature(impl_trait_in_bindings)]
+//~^ WARN the feature `impl_trait_in_bindings` is incomplete and may cause the compiler to crash
 
 const FOO: impl Copy = 42;
 
diff --git a/src/test/ui/impl-trait/bindings-opaque.stderr b/src/test/ui/impl-trait/bindings-opaque.stderr
index 8b2514c0501..d0a6a4ee578 100644
--- a/src/test/ui/impl-trait/bindings-opaque.stderr
+++ b/src/test/ui/impl-trait/bindings-opaque.stderr
@@ -1,17 +1,23 @@
+warning: the feature `impl_trait_in_bindings` is incomplete and may cause the compiler to crash
+  --> $DIR/bindings-opaque.rs:1:12
+   |
+LL | #![feature(impl_trait_in_bindings)]
+   |            ^^^^^^^^^^^^^^^^^^^^^^
+
 error[E0599]: no method named `count_ones` found for type `impl std::marker::Copy` in the current scope
-  --> $DIR/bindings-opaque.rs:10:17
+  --> $DIR/bindings-opaque.rs:11:17
    |
 LL |     let _ = FOO.count_ones();
    |                 ^^^^^^^^^^
 
 error[E0599]: no method named `count_ones` found for type `impl std::marker::Copy` in the current scope
-  --> $DIR/bindings-opaque.rs:12:17
+  --> $DIR/bindings-opaque.rs:13:17
    |
 LL |     let _ = BAR.count_ones();
    |                 ^^^^^^^^^^
 
 error[E0599]: no method named `count_ones` found for type `impl std::marker::Copy` in the current scope
-  --> $DIR/bindings-opaque.rs:14:17
+  --> $DIR/bindings-opaque.rs:15:17
    |
 LL |     let _ = foo.count_ones();
    |                 ^^^^^^^^^^
diff --git a/src/test/ui/impl-trait/bindings.rs b/src/test/ui/impl-trait/bindings.rs
index 91d092634a9..104a44d6566 100644
--- a/src/test/ui/impl-trait/bindings.rs
+++ b/src/test/ui/impl-trait/bindings.rs
@@ -1,4 +1,5 @@
 #![feature(impl_trait_in_bindings)]
+//~^ WARN the feature `impl_trait_in_bindings` is incomplete and may cause the compiler to crash
 
 fn a<T: Clone>(x: T) {
     const foo: impl Clone = x;
diff --git a/src/test/ui/impl-trait/bindings.stderr b/src/test/ui/impl-trait/bindings.stderr
index a5bf583afea..c66836ab8e5 100644
--- a/src/test/ui/impl-trait/bindings.stderr
+++ b/src/test/ui/impl-trait/bindings.stderr
@@ -1,23 +1,29 @@
+warning: the feature `impl_trait_in_bindings` is incomplete and may cause the compiler to crash
+  --> $DIR/bindings.rs:1:12
+   |
+LL | #![feature(impl_trait_in_bindings)]
+   |            ^^^^^^^^^^^^^^^^^^^^^^
+
 error[E0435]: attempt to use a non-constant value in a constant
-  --> $DIR/bindings.rs:4:29
+  --> $DIR/bindings.rs:5:29
    |
 LL |     const foo: impl Clone = x;
    |                             ^ non-constant value
 
 error[E0435]: attempt to use a non-constant value in a constant
-  --> $DIR/bindings.rs:10:33
+  --> $DIR/bindings.rs:11:33
    |
 LL |         const foo: impl Clone = x;
    |                                 ^ non-constant value
 
 error[E0435]: attempt to use a non-constant value in a constant
-  --> $DIR/bindings.rs:17:33
+  --> $DIR/bindings.rs:18:33
    |
 LL |         const foo: impl Clone = x;
    |                                 ^ non-constant value
 
 error[E0435]: attempt to use a non-constant value in a constant
-  --> $DIR/bindings.rs:24:33
+  --> $DIR/bindings.rs:25:33
    |
 LL |         const foo: impl Clone = x;
    |                                 ^ non-constant value