diff --git a/src/libcore/macros.rs b/src/libcore/macros.rs
index bf4e414d416..320d3236840 100644
--- a/src/libcore/macros.rs
+++ b/src/libcore/macros.rs
@@ -542,7 +542,8 @@ macro_rules! unreachable {
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
 macro_rules! unimplemented {
-    () => (panic!("not yet implemented"))
+    () => (panic!("not yet implemented"));
+    ($($arg:tt)+) => (panic!("not yet implemented: {}", format_args!($($arg)*)));
 }
 
 /// Built-in macros to the compiler itself.