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diff --git a/compiler/rustc_error_codes/src/error_codes/E0281.md b/compiler/rustc_error_codes/src/error_codes/E0281.md
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+#### Note: this error code is no longer emitted by the compiler.
+
+You tried to supply a type which doesn't implement some trait in a location
+which expected that trait. This error typically occurs when working with
+`Fn`-based types. Erroneous code example:
+
+```compile_fail
+fn foo<F: Fn(usize)>(x: F) { }
+
+fn main() {
+    // type mismatch: ... implements the trait `core::ops::Fn<(String,)>`,
+    // but the trait `core::ops::Fn<(usize,)>` is required
+    // [E0281]
+    foo(|y: String| { });
+}
+```
+
+The issue in this case is that `foo` is defined as accepting a `Fn` with one
+argument of type `String`, but the closure we attempted to pass to it requires
+one arguments of type `usize`.