diff --git a/tests/source/issue_4257.rs b/tests/source/issue_4257.rs
new file mode 100644
index 00000000000..2b887fadb62
--- /dev/null
+++ b/tests/source/issue_4257.rs
@@ -0,0 +1,13 @@
+#![feature(generic_associated_types)]
+#![allow(incomplete_features)]
+
+trait Trait<T> {
+    type Type<'a> where T: 'a;
+    fn foo(x: &T) -> Self::Type<'_>;
+}
+impl<T> Trait<T> for () {
+    type Type<'a> where T: 'a = &'a T;
+    fn foo(x: &T) -> Self::Type<'_> {
+        x
+    }
+}
diff --git a/tests/target/issue_4257.rs b/tests/target/issue_4257.rs
new file mode 100644
index 00000000000..1ebaaf2b600
--- /dev/null
+++ b/tests/target/issue_4257.rs
@@ -0,0 +1,18 @@
+#![feature(generic_associated_types)]
+#![allow(incomplete_features)]
+
+trait Trait<T> {
+    type Type<'a>
+    where
+        T: 'a;
+    fn foo(x: &T) -> Self::Type<'_>;
+}
+impl<T> Trait<T> for () {
+    type Type<'a>
+    where
+        T: 'a,
+    = &'a T;
+    fn foo(x: &T) -> Self::Type<'_> {
+        x
+    }
+}