diff --git a/src/intrinsic.rs b/src/intrinsic.rs
index 5c86075883..9ccffc7b8f 100644
--- a/src/intrinsic.rs
+++ b/src/intrinsic.rs
@@ -423,7 +423,8 @@ impl<'a, 'mir, 'tcx> EvalContextExt<'tcx> for super::MiriEvalContext<'a, 'mir, '
                             // Do it in memory
                             let mplace = self.force_allocation(dest)?;
                             assert!(mplace.meta.is_none());
-                            self.memory.mark_definedness(mplace.ptr.to_ptr()?, dest.layout.size, false)?;
+                            let ptr = mplace.ptr.to_ptr()?;
+                            self.memory.get_mut(ptr.alloc_id)?.mark_definedness(ptr, dest.layout.size, false)?;
                         }
                     }
                 }
diff --git a/src/lib.rs b/src/lib.rs
index ed23eef3f5..39cac10fd4 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -422,16 +422,6 @@ impl<'a, 'mir, 'tcx> Machine<'a, 'mir, 'tcx> for Evaluator<'tcx> {
         Cow::Owned(alloc)
     }
 
-    #[inline(always)]
-    fn memory_accessed(
-        alloc: &Allocation<Borrow, Self::AllocExtra>,
-        ptr: Pointer<Borrow>,
-        size: Size,
-        access: MemoryAccess,
-    ) -> EvalResult<'tcx> {
-        alloc.extra.memory_accessed(ptr, size, access)
-    }
-
     #[inline(always)]
     fn memory_deallocated(
         alloc: &mut Allocation<Self::PointerTag, Self::AllocExtra>,
diff --git a/src/operator.rs b/src/operator.rs
index a11f8f34e7..a8ca0b7a78 100644
--- a/src/operator.rs
+++ b/src/operator.rs
@@ -142,8 +142,8 @@ impl<'a, 'mir, 'tcx> EvalContextExt<'tcx> for super::MiriEvalContext<'a, 'mir, '
                     // allocations sit right next to each other.  The C/C++ standards are
                     // somewhat fuzzy about this case, so I think for now this check is
                     // "good enough".
-                    self.memory.check_bounds_ptr(left, false)?;
-                    self.memory.check_bounds_ptr(right, false)?;
+                    self.memory.get(left.alloc_id)?.check_bounds_ptr(left, false)?;
+                    self.memory.get(right.alloc_id)?.check_bounds_ptr(right, false)?;
                     // Two live in-bounds pointers, we can compare across allocations
                     left == right
                 }
@@ -295,9 +295,9 @@ impl<'a, 'mir, 'tcx> EvalContextExt<'tcx> for super::MiriEvalContext<'a, 'mir, '
         if let Scalar::Ptr(ptr) = ptr {
             // Both old and new pointer must be in-bounds.
             // (Of the same allocation, but that part is trivial with our representation.)
-            self.memory.check_bounds_ptr(ptr, false)?;
+            self.memory.get(ptr.alloc_id)?.check_bounds_ptr(ptr, false)?;
             let ptr = ptr.signed_offset(offset, self)?;
-            self.memory.check_bounds_ptr(ptr, false)?;
+            self.memory.get(ptr.alloc_id)?.check_bounds_ptr(ptr, false)?;
             Ok(Scalar::Ptr(ptr))
         } else {
             // An integer pointer. They can only be offset by 0, and we pretend there
diff --git a/src/stacked_borrows.rs b/src/stacked_borrows.rs
index 077deceecf..76179b1c55 100644
--- a/src/stacked_borrows.rs
+++ b/src/stacked_borrows.rs
@@ -5,7 +5,7 @@ use rustc::mir;
 
 use super::{
     MemoryAccess, RangeMap, EvalResult,
-    Pointer,
+    Pointer, AllocationExtra,
 };
 
 pub type Timestamp = u64;
@@ -187,8 +187,9 @@ impl State {
 }
 
 /// Higher-level operations
-impl<'tcx> Stacks {
-    pub fn memory_accessed(
+impl AllocationExtra<Borrow> for Stacks {
+    #[inline(always)]
+    fn memory_accessed<'tcx>(
         &self,
         ptr: Pointer<Borrow>,
         size: Size,
@@ -202,7 +203,10 @@ impl<'tcx> Stacks {
         }
         Ok(())
     }
+}
 
+/// Higher-level operations
+impl<'tcx> Stacks {
     pub fn memory_deallocated(
         &mut self,
         ptr: Pointer<Borrow>,