diff --git a/src/test/run-pass/existential_type.rs b/src/test/run-pass/existential_type.rs
index d2cecd83036e..e63d5c2293a8 100644
--- a/src/test/run-pass/existential_type.rs
+++ b/src/test/run-pass/existential_type.rs
@@ -75,10 +75,10 @@ fn my_other_iter<U>(u: U) -> MyOtherIter<U> {
 }
 
 trait Trait {}
-existential type GenericBound<T: Trait>: 'static;
+existential type GenericBound<'a, T: Trait>: 'a;
 
-fn generic_bound<T: Trait>(_: T) -> GenericBound<T> {
-    unimplemented!()
+fn generic_bound<'a, T: Trait + 'a>(t: T) -> GenericBound<'a, T> {
+    t
 }
 
 mod pass_through {
@@ -92,22 +92,3 @@ mod pass_through {
 fn use_passthrough(x: pass_through::Passthrough<u32>) -> pass_through::Passthrough<u32> {
     x
 }
-
-existential type PartiallyDefined<T>: 'static;
-
-// doesn't declare all PartiallyDefined for all possible `T`, but since it's the only
-// function producing the value, noone can ever get a value that is problematic
-fn partially_defined<T: std::fmt::Debug>(_: T) -> PartiallyDefined<T> {
-    4u32
-}
-
-existential type PartiallyDefined2<T>: 'static;
-
-fn partially_defined2<T: std::fmt::Debug>(_: T) -> PartiallyDefined2<T> {
-    4u32
-}
-
-// fully defines PartiallyDefine2
-fn partially_defined22<T>(_: T) -> PartiallyDefined2<T> {
-    4u32
-}
diff --git a/src/test/ui/existential_types/unused_generic_param.rs b/src/test/ui/existential_types/unused_generic_param.rs
new file mode 100644
index 000000000000..420ce89cc37c
--- /dev/null
+++ b/src/test/ui/existential_types/unused_generic_param.rs
@@ -0,0 +1,30 @@
+// Copyright 2018 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.
+
+#![feature(existential_type)]
+
+fn main() {
+}
+
+existential type PartiallyDefined<T>: 'static; //~ `T` is unused
+
+fn partially_defined<T: std::fmt::Debug>(_: T) -> PartiallyDefined<T> {
+    4u32
+}
+
+existential type PartiallyDefined2<T>: 'static; //~ `T` is unused
+
+fn partially_defined2<T: std::fmt::Debug>(_: T) -> PartiallyDefined2<T> {
+    4u32
+}
+
+fn partially_defined22<T>(_: T) -> PartiallyDefined2<T> {
+    4u32
+}
diff --git a/src/test/ui/existential_types/unused_generic_param.stderr b/src/test/ui/existential_types/unused_generic_param.stderr
new file mode 100644
index 000000000000..7ad5eab0b0a6
--- /dev/null
+++ b/src/test/ui/existential_types/unused_generic_param.stderr
@@ -0,0 +1,15 @@
+error[E0091]: type parameter `T` is unused
+  --> $DIR/unused_generic_param.rs:16:35
+   |
+LL | existential type PartiallyDefined<T>: 'static; //~ `T` is unused
+   |                                   ^ unused type parameter
+
+error[E0091]: type parameter `T` is unused
+  --> $DIR/unused_generic_param.rs:22:36
+   |
+LL | existential type PartiallyDefined2<T>: 'static; //~ `T` is unused
+   |                                    ^ unused type parameter
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0091`.