diff --git a/src/libcore/fmt/num.rs b/src/libcore/fmt/num.rs
index ee989854a3772..2992e7cf8db34 100644
--- a/src/libcore/fmt/num.rs
+++ b/src/libcore/fmt/num.rs
@@ -157,6 +157,7 @@ macro_rules! debug {
     ($T:ident) => {
         #[stable(feature = "rust1", since = "1.0.0")]
         impl fmt::Debug for $T {
+            #[inline]
             fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                 fmt::Display::fmt(self, f)
             }