diff --git a/src/librustc_plugin/registry.rs b/src/librustc_plugin/registry.rs
index 3027489d65be2..2ea7bcbdb2317 100644
--- a/src/librustc_plugin/registry.rs
+++ b/src/librustc_plugin/registry.rs
@@ -113,17 +113,6 @@ impl<'a> Registry<'a> {
         }));
     }
 
-    /// This can be used in place of `register_syntax_extension` to register legacy custom derives
-    /// (i.e. attribute syntax extensions whose name begins with `derive_`). Legacy custom
-    /// derives defined by this function do not trigger deprecation warnings when used.
-    #[unstable(feature = "rustc_private", issue = "27812")]
-    #[rustc_deprecated(since = "1.15.0", reason = "replaced by macros 1.1 (RFC 1861)")]
-    pub fn register_custom_derive(&mut self, name: ast::Name, extension: SyntaxExtension) {
-        assert!(name.as_str().starts_with("derive_"));
-        self.whitelisted_custom_derives.push(name);
-        self.register_syntax_extension(name, extension);
-    }
-
     pub fn take_whitelisted_custom_derives(&mut self) -> Vec<ast::Name> {
         ::std::mem::replace(&mut self.whitelisted_custom_derives, Vec::new())
     }