diff --git a/src/liballoc/collections/mod.rs b/src/liballoc/collections/mod.rs
index 48c3ed8a57d86..f1f22fe48c58a 100644
--- a/src/liballoc/collections/mod.rs
+++ b/src/liballoc/collections/mod.rs
@@ -41,25 +41,28 @@ pub use linked_list::LinkedList;
 #[doc(no_inline)]
 pub use vec_deque::VecDeque;
 
-use crate::alloc::{AllocErr, LayoutErr};
+use crate::alloc::{Layout, LayoutErr};
 
-/// Augments `AllocErr` with a CapacityOverflow variant.
+/// The error type for `try_reserve` methods.
 #[derive(Clone, PartialEq, Eq, Debug)]
 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
 pub enum TryReserveError {
     /// Error due to the computed capacity exceeding the collection's maximum
     /// (usually `isize::MAX` bytes).
     CapacityOverflow,
-    /// Error due to the allocator (see the `AllocErr` type's docs).
-    AllocErr,
-}
 
-#[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
-impl From<AllocErr> for TryReserveError {
-    #[inline]
-    fn from(AllocErr: AllocErr) -> Self {
-        TryReserveError::AllocErr
-    }
+    /// The memory allocator returned an error
+    AllocError {
+        /// The layout of allocation request that failed
+        layout: Layout,
+
+        #[doc(hidden)]
+        #[unstable(feature = "container_error_extra", issue = "0", reason = "\
+            Enable exposing the allocator’s custom error value \
+            if an associated type is added in the future: \
+            https://github.com/rust-lang/wg-allocators/issues/23")]
+        non_exhaustive: (),
+    },
 }
 
 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
diff --git a/src/liballoc/lib.rs b/src/liballoc/lib.rs
index 7421beddd9574..4a48945adc37a 100644
--- a/src/liballoc/lib.rs
+++ b/src/liballoc/lib.rs
@@ -87,6 +87,7 @@
 #![feature(const_in_array_repeat_expressions)]
 #![feature(dispatch_from_dyn)]
 #![feature(core_intrinsics)]
+#![feature(container_error_extra)]
 #![feature(dropck_eyepatch)]
 #![feature(exact_size_is_empty)]
 #![feature(fmt_internals)]
diff --git a/src/liballoc/raw_vec.rs b/src/liballoc/raw_vec.rs
index fed5a16599d58..bc8a38f6b3aad 100644
--- a/src/liballoc/raw_vec.rs
+++ b/src/liballoc/raw_vec.rs
@@ -7,7 +7,7 @@ use core::ops::Drop;
 use core::ptr::{self, NonNull, Unique};
 use core::slice;
 
-use crate::alloc::{Alloc, Layout, Global, handle_alloc_error};
+use crate::alloc::{Alloc, Layout, Global, AllocErr, handle_alloc_error};
 use crate::collections::TryReserveError::{self, *};
 use crate::boxed::Box;
 
@@ -413,7 +413,7 @@ impl<T, A: Alloc> RawVec<T, A> {
     pub fn reserve_exact(&mut self, used_capacity: usize, needed_extra_capacity: usize) {
         match self.reserve_internal(used_capacity, needed_extra_capacity, Infallible, Exact) {
             Err(CapacityOverflow) => capacity_overflow(),
-            Err(AllocErr) => unreachable!(),
+            Err(AllocError { .. }) => unreachable!(),
             Ok(()) => { /* yay */ }
          }
      }
@@ -494,7 +494,7 @@ impl<T, A: Alloc> RawVec<T, A> {
     pub fn reserve(&mut self, used_capacity: usize, needed_extra_capacity: usize) {
         match self.reserve_internal(used_capacity, needed_extra_capacity, Infallible, Amortized) {
             Err(CapacityOverflow) => capacity_overflow(),
-            Err(AllocErr) => unreachable!(),
+            Err(AllocError { .. }) => unreachable!(),
             Ok(()) => { /* yay */ }
         }
     }
@@ -642,8 +642,6 @@ impl<T, A: Alloc> RawVec<T, A> {
         strategy: ReserveStrategy,
     ) -> Result<(), TryReserveError> {
         unsafe {
-            use crate::alloc::AllocErr;
-
             // NOTE: we don't early branch on ZSTs here because we want this
             // to actually catch "asking for more than usize::MAX" in that case.
             // If we make it past the first branch then we are guaranteed to
@@ -672,12 +670,16 @@ impl<T, A: Alloc> RawVec<T, A> {
                 None => self.a.alloc(new_layout),
             };
 
-            match (&res, fallibility) {
+            let ptr = match (res, fallibility) {
                 (Err(AllocErr), Infallible) => handle_alloc_error(new_layout),
-                _ => {}
-            }
+                (Err(AllocErr), Fallible) => return Err(TryReserveError::AllocError {
+                    layout: new_layout,
+                    non_exhaustive: (),
+                }),
+                (Ok(ptr), _) => ptr,
+            };
 
-            self.ptr = res?.cast().into();
+            self.ptr = ptr.cast().into();
             self.cap = new_cap;
 
             Ok(())
diff --git a/src/liballoc/tests/string.rs b/src/liballoc/tests/string.rs
index 4d2ea42fcaea5..55edf56345b59 100644
--- a/src/liballoc/tests/string.rs
+++ b/src/liballoc/tests/string.rs
@@ -566,11 +566,11 @@ fn test_try_reserve() {
             } else { panic!("usize::MAX should trigger an overflow!") }
         } else {
             // Check isize::MAX + 1 is an OOM
-            if let Err(AllocErr) = empty_string.try_reserve(MAX_CAP + 1) {
+            if let Err(AllocError { .. }) = empty_string.try_reserve(MAX_CAP + 1) {
             } else { panic!("isize::MAX + 1 should trigger an OOM!") }
 
             // Check usize::MAX is an OOM
-            if let Err(AllocErr) = empty_string.try_reserve(MAX_USIZE) {
+            if let Err(AllocError { .. }) = empty_string.try_reserve(MAX_USIZE) {
             } else { panic!("usize::MAX should trigger an OOM!") }
         }
     }
@@ -590,7 +590,7 @@ fn test_try_reserve() {
             if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 9) {
             } else { panic!("isize::MAX + 1 should trigger an overflow!"); }
         } else {
-            if let Err(AllocErr) = ten_bytes.try_reserve(MAX_CAP - 9) {
+            if let Err(AllocError { .. }) = ten_bytes.try_reserve(MAX_CAP - 9) {
             } else { panic!("isize::MAX + 1 should trigger an OOM!") }
         }
         // Should always overflow in the add-to-len
@@ -629,10 +629,10 @@ fn test_try_reserve_exact() {
             if let Err(CapacityOverflow) = empty_string.try_reserve_exact(MAX_USIZE) {
             } else { panic!("usize::MAX should trigger an overflow!") }
         } else {
-            if let Err(AllocErr) = empty_string.try_reserve_exact(MAX_CAP + 1) {
+            if let Err(AllocError { .. }) = empty_string.try_reserve_exact(MAX_CAP + 1) {
             } else { panic!("isize::MAX + 1 should trigger an OOM!") }
 
-            if let Err(AllocErr) = empty_string.try_reserve_exact(MAX_USIZE) {
+            if let Err(AllocError { .. }) = empty_string.try_reserve_exact(MAX_USIZE) {
             } else { panic!("usize::MAX should trigger an OOM!") }
         }
     }
@@ -651,7 +651,7 @@ fn test_try_reserve_exact() {
             if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_CAP - 9) {
             } else { panic!("isize::MAX + 1 should trigger an overflow!"); }
         } else {
-            if let Err(AllocErr) = ten_bytes.try_reserve_exact(MAX_CAP - 9) {
+            if let Err(AllocError { .. }) = ten_bytes.try_reserve_exact(MAX_CAP - 9) {
             } else { panic!("isize::MAX + 1 should trigger an OOM!") }
         }
         if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_USIZE) {
diff --git a/src/liballoc/tests/vec.rs b/src/liballoc/tests/vec.rs
index c67ec32543b7b..29a22aa0315b0 100644
--- a/src/liballoc/tests/vec.rs
+++ b/src/liballoc/tests/vec.rs
@@ -1121,11 +1121,11 @@ fn test_try_reserve() {
             } else { panic!("usize::MAX should trigger an overflow!") }
         } else {
             // Check isize::MAX + 1 is an OOM
-            if let Err(AllocErr) = empty_bytes.try_reserve(MAX_CAP + 1) {
+            if let Err(AllocError { .. }) = empty_bytes.try_reserve(MAX_CAP + 1) {
             } else { panic!("isize::MAX + 1 should trigger an OOM!") }
 
             // Check usize::MAX is an OOM
-            if let Err(AllocErr) = empty_bytes.try_reserve(MAX_USIZE) {
+            if let Err(AllocError { .. }) = empty_bytes.try_reserve(MAX_USIZE) {
             } else { panic!("usize::MAX should trigger an OOM!") }
         }
     }
@@ -1145,7 +1145,7 @@ fn test_try_reserve() {
             if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 9) {
             } else { panic!("isize::MAX + 1 should trigger an overflow!"); }
         } else {
-            if let Err(AllocErr) = ten_bytes.try_reserve(MAX_CAP - 9) {
+            if let Err(AllocError { .. }) = ten_bytes.try_reserve(MAX_CAP - 9) {
             } else { panic!("isize::MAX + 1 should trigger an OOM!") }
         }
         // Should always overflow in the add-to-len
@@ -1168,7 +1168,7 @@ fn test_try_reserve() {
             if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_CAP/4 - 9) {
             } else { panic!("isize::MAX + 1 should trigger an overflow!"); }
         } else {
-            if let Err(AllocErr) = ten_u32s.try_reserve(MAX_CAP/4 - 9) {
+            if let Err(AllocError { .. }) = ten_u32s.try_reserve(MAX_CAP/4 - 9) {
             } else { panic!("isize::MAX + 1 should trigger an OOM!") }
         }
         // Should fail in the mul-by-size
@@ -1209,10 +1209,10 @@ fn test_try_reserve_exact() {
             if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_USIZE) {
             } else { panic!("usize::MAX should trigger an overflow!") }
         } else {
-            if let Err(AllocErr) = empty_bytes.try_reserve_exact(MAX_CAP + 1) {
+            if let Err(AllocError { .. }) = empty_bytes.try_reserve_exact(MAX_CAP + 1) {
             } else { panic!("isize::MAX + 1 should trigger an OOM!") }
 
-            if let Err(AllocErr) = empty_bytes.try_reserve_exact(MAX_USIZE) {
+            if let Err(AllocError { .. }) = empty_bytes.try_reserve_exact(MAX_USIZE) {
             } else { panic!("usize::MAX should trigger an OOM!") }
         }
     }
@@ -1231,7 +1231,7 @@ fn test_try_reserve_exact() {
             if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_CAP - 9) {
             } else { panic!("isize::MAX + 1 should trigger an overflow!"); }
         } else {
-            if let Err(AllocErr) = ten_bytes.try_reserve_exact(MAX_CAP - 9) {
+            if let Err(AllocError { .. }) = ten_bytes.try_reserve_exact(MAX_CAP - 9) {
             } else { panic!("isize::MAX + 1 should trigger an OOM!") }
         }
         if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_USIZE) {
@@ -1252,7 +1252,7 @@ fn test_try_reserve_exact() {
             if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_CAP/4 - 9) {
             } else { panic!("isize::MAX + 1 should trigger an overflow!"); }
         } else {
-            if let Err(AllocErr) = ten_u32s.try_reserve_exact(MAX_CAP/4 - 9) {
+            if let Err(AllocError { .. }) = ten_u32s.try_reserve_exact(MAX_CAP/4 - 9) {
             } else { panic!("isize::MAX + 1 should trigger an OOM!") }
         }
         if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_USIZE - 20) {
diff --git a/src/liballoc/tests/vec_deque.rs b/src/liballoc/tests/vec_deque.rs
index c7e743c2e945e..d49b553fc0217 100644
--- a/src/liballoc/tests/vec_deque.rs
+++ b/src/liballoc/tests/vec_deque.rs
@@ -1168,7 +1168,7 @@ fn test_try_reserve() {
             // VecDeque starts with capacity 7, always adds 1 to the capacity
             // and also rounds the number to next power of 2 so this is the
             // furthest we can go without triggering CapacityOverflow
-            if let Err(AllocErr) = empty_bytes.try_reserve(MAX_CAP) {
+            if let Err(AllocError { .. }) = empty_bytes.try_reserve(MAX_CAP) {
             } else { panic!("isize::MAX + 1 should trigger an OOM!") }
         }
     }
@@ -1188,7 +1188,7 @@ fn test_try_reserve() {
             if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 9) {
             } else { panic!("isize::MAX + 1 should trigger an overflow!"); }
         } else {
-            if let Err(AllocErr) = ten_bytes.try_reserve(MAX_CAP - 9) {
+            if let Err(AllocError { .. }) = ten_bytes.try_reserve(MAX_CAP - 9) {
             } else { panic!("isize::MAX + 1 should trigger an OOM!") }
         }
         // Should always overflow in the add-to-len
@@ -1211,7 +1211,7 @@ fn test_try_reserve() {
             if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_CAP/4 - 9) {
             } else { panic!("isize::MAX + 1 should trigger an overflow!"); }
         } else {
-            if let Err(AllocErr) = ten_u32s.try_reserve(MAX_CAP/4 - 9) {
+            if let Err(AllocError { .. }) = ten_u32s.try_reserve(MAX_CAP/4 - 9) {
             } else { panic!("isize::MAX + 1 should trigger an OOM!") }
         }
         // Should fail in the mul-by-size
@@ -1256,7 +1256,7 @@ fn test_try_reserve_exact() {
             // VecDeque starts with capacity 7, always adds 1 to the capacity
             // and also rounds the number to next power of 2 so this is the
             // furthest we can go without triggering CapacityOverflow
-            if let Err(AllocErr) = empty_bytes.try_reserve_exact(MAX_CAP) {
+            if let Err(AllocError { .. }) = empty_bytes.try_reserve_exact(MAX_CAP) {
             } else { panic!("isize::MAX + 1 should trigger an OOM!") }
         }
     }
@@ -1275,7 +1275,7 @@ fn test_try_reserve_exact() {
             if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_CAP - 9) {
             } else { panic!("isize::MAX + 1 should trigger an overflow!"); }
         } else {
-            if let Err(AllocErr) = ten_bytes.try_reserve_exact(MAX_CAP - 9) {
+            if let Err(AllocError { .. }) = ten_bytes.try_reserve_exact(MAX_CAP - 9) {
             } else { panic!("isize::MAX + 1 should trigger an OOM!") }
         }
         if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_USIZE) {
@@ -1296,7 +1296,7 @@ fn test_try_reserve_exact() {
             if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_CAP/4 - 9) {
             } else { panic!("isize::MAX + 1 should trigger an overflow!"); }
         } else {
-            if let Err(AllocErr) = ten_u32s.try_reserve_exact(MAX_CAP/4 - 9) {
+            if let Err(AllocError { .. }) = ten_u32s.try_reserve_exact(MAX_CAP/4 - 9) {
             } else { panic!("isize::MAX + 1 should trigger an OOM!") }
         }
         if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_USIZE - 20) {
diff --git a/src/libstd/collections/hash/map.rs b/src/libstd/collections/hash/map.rs
index db637a108cba8..a0538986a2242 100644
--- a/src/libstd/collections/hash/map.rs
+++ b/src/libstd/collections/hash/map.rs
@@ -2545,7 +2545,10 @@ fn map_entry<'a, K: 'a, V: 'a>(raw: base::RustcEntry<'a, K, V>) -> Entry<'a, K,
 fn map_collection_alloc_err(err: hashbrown::CollectionAllocErr) -> TryReserveError {
     match err {
         hashbrown::CollectionAllocErr::CapacityOverflow => TryReserveError::CapacityOverflow,
-        hashbrown::CollectionAllocErr::AllocErr { .. } => TryReserveError::AllocErr,
+        hashbrown::CollectionAllocErr::AllocErr { layout } => TryReserveError::AllocError {
+            layout,
+            non_exhaustive: (),
+        },
     }
 }
 
@@ -3405,7 +3408,7 @@ mod test_map {
             panic!("usize::MAX should trigger an overflow!");
         }
 
-        if let Err(AllocErr) = empty_bytes.try_reserve(MAX_USIZE / 8) {
+        if let Err(AllocError { .. }) = empty_bytes.try_reserve(MAX_USIZE / 8) {
         } else {
             panic!("usize::MAX / 8 should trigger an OOM!")
         }
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index 1f48315d3f8db..760d92f1d7b0e 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -251,6 +251,7 @@
 #![feature(concat_idents)]
 #![feature(const_cstr_unchecked)]
 #![feature(const_raw_ptr_deref)]
+#![feature(container_error_extra)]
 #![feature(core_intrinsics)]
 #![feature(custom_test_frameworks)]
 #![feature(doc_alias)]