diff --git a/library/alloc/src/alloc.rs b/library/alloc/src/alloc.rs
index 341c6816197..7d872b1a66b 100644
--- a/library/alloc/src/alloc.rs
+++ b/library/alloc/src/alloc.rs
@@ -145,7 +145,7 @@ pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
 
 impl Global {
     #[inline]
-    fn alloc_impl(&mut self, layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocErr> {
+    fn alloc_impl(&self, layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocErr> {
         match layout.size() {
             0 => Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0)),
             // SAFETY: `layout` is non-zero in size,
@@ -208,7 +208,7 @@ impl Global {
 #[unstable(feature = "allocator_api", issue = "32838")]
 unsafe impl AllocRef for Global {
     #[inline]
-    fn alloc(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
+    fn alloc(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
         self.alloc_impl(layout, false)
     }
 
diff --git a/library/alloc/src/raw_vec/tests.rs b/library/alloc/src/raw_vec/tests.rs
index cadd913aa6b..f348710d61a 100644
--- a/library/alloc/src/raw_vec/tests.rs
+++ b/library/alloc/src/raw_vec/tests.rs
@@ -1,4 +1,5 @@
 use super::*;
+use std::cell::Cell;
 
 #[test]
 fn allocator_param() {
@@ -17,17 +18,17 @@ fn allocator_param() {
     // A dumb allocator that consumes a fixed amount of fuel
     // before allocation attempts start failing.
     struct BoundedAlloc {
-        fuel: usize,
+        fuel: Cell<usize>,
     }
     unsafe impl AllocRef for BoundedAlloc {
-        fn alloc(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
+        fn alloc(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
             let size = layout.size();
-            if size > self.fuel {
+            if size > self.fuel.get() {
                 return Err(AllocErr);
             }
             match Global.alloc(layout) {
                 ok @ Ok(_) => {
-                    self.fuel -= size;
+                    self.fuel.update(|old| old - size);
                     ok
                 }
                 err @ Err(_) => err,
@@ -38,11 +39,11 @@ fn allocator_param() {
         }
     }
 
-    let a = BoundedAlloc { fuel: 500 };
+    let a = BoundedAlloc { fuel: Cell::new(500) };
     let mut v: RawVec<u8, _> = RawVec::with_capacity_in(50, a);
-    assert_eq!(v.alloc.fuel, 450);
+    assert_eq!(v.alloc.fuel.get(), 450);
     v.reserve(50, 150); // (causes a realloc, thus using 50 + 150 = 200 units of fuel)
-    assert_eq!(v.alloc.fuel, 250);
+    assert_eq!(v.alloc.fuel.get(), 250);
 }
 
 #[test]
diff --git a/library/core/src/alloc/mod.rs b/library/core/src/alloc/mod.rs
index c1fda2fce64..b7dd249d093 100644
--- a/library/core/src/alloc/mod.rs
+++ b/library/core/src/alloc/mod.rs
@@ -109,7 +109,7 @@ pub unsafe trait AllocRef {
     /// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar.
     ///
     /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
-    fn alloc(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr>;
+    fn alloc(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr>;
 
     /// Behaves like `alloc`, but also ensures that the returned memory is zero-initialized.
     ///
@@ -348,7 +348,7 @@ where
     A: AllocRef + ?Sized,
 {
     #[inline]
-    fn alloc(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
+    fn alloc(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
         (**self).alloc(layout)
     }
 
diff --git a/library/std/src/alloc.rs b/library/std/src/alloc.rs
index 770c97899f0..86ae4cf4dd2 100644
--- a/library/std/src/alloc.rs
+++ b/library/std/src/alloc.rs
@@ -133,7 +133,7 @@ pub struct System;
 
 impl System {
     #[inline]
-    fn alloc_impl(&mut self, layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocErr> {
+    fn alloc_impl(&self, layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocErr> {
         match layout.size() {
             0 => Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0)),
             // SAFETY: `layout` is non-zero in size,
@@ -202,7 +202,7 @@ impl System {
 #[unstable(feature = "allocator_api", issue = "32838")]
 unsafe impl AllocRef for System {
     #[inline]
-    fn alloc(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
+    fn alloc(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
         self.alloc_impl(layout, false)
     }
 
diff --git a/src/test/ui/allocator/custom.rs b/src/test/ui/allocator/custom.rs
index a6c2317c736..603f59ab069 100644
--- a/src/test/ui/allocator/custom.rs
+++ b/src/test/ui/allocator/custom.rs
@@ -18,7 +18,7 @@ struct A;
 unsafe impl alloc::GlobalAlloc for A {
     unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
         HITS.fetch_add(1, Ordering::SeqCst);
-        System.alloc(layout)
+        AllocRef::alloc(&System, layout).unwrap().as_mut_ptr()
     }
 
     unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {