diff --git a/src/libcore/alloc.rs b/src/libcore/alloc.rs
index 8f8849e32e6cb..22c674363789b 100644
--- a/src/libcore/alloc.rs
+++ b/src/libcore/alloc.rs
@@ -380,6 +380,7 @@ pub enum CollectionAllocErr {
 
 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
 impl From<AllocErr> for CollectionAllocErr {
+    #[inline]
     fn from(AllocErr: AllocErr) -> Self {
         CollectionAllocErr::AllocErr
     }