diff --git a/mlton/backend/allocate-variables.fun b/mlton/backend/allocate-variables.fun
index 191222c6f..e380ded29 100644
--- a/mlton/backend/allocate-variables.fun
+++ b/mlton/backend/allocate-variables.fun
@@ -1,4 +1,4 @@
-(* Copyright (C) 2017,2019,2022 Matthew Fluet.
+(* Copyright (C) 2017,2019,2022-2023 Matthew Fluet.
  * Copyright (C) 1999-2007 Henry Cejtin, Matthew Fluet, Suresh
  *    Jagannathan, and Stephen Weeks.
  * Copyright (C) 1997-2000 NEC Research Institute.
@@ -102,7 +102,9 @@ structure Allocation:
                     | (a1 as {offset = offset1, size = size1})::(a2 as {offset = offset2, size = size2})::alloc =>
                          if Bytes.equals (Bytes.+ (offset1, size1), offset2)
                             then loop ({offset = offset1, size = Bytes.+ (size1, size2)}::alloc, ac)
-                            else loop (a2::alloc, a1::ac)
+                            else if Bytes.> (Bytes.+ (offset1, size1), offset2)
+                                    then Error.bug "AllocateVariables.Stack.new"
+                                    else loop (a2::alloc, a1::ac)
              in
                 T (loop (Array.toList a, []))
              end
@@ -461,8 +463,8 @@ fun allocate {function = f: Rssa.Function.t,
                    *)
                   val (stack, {offset = linkOffset, ...}) =
                      Allocation.Stack.get (stack, Type.exnStack ())
-                  val (_, {offset = handlerOffset, ...}) =
-                     Allocation.Stack.get (stack, Type.label (Label.newNoname ()))
+                  val handlerTy = Type.label (Label.newNoname ())
+                  val handlerOffset = Type.align (handlerTy, Allocation.Stack.size stack)
                   val handlerArgsOffset =
                      Bytes.align
                      (Bytes.+ (handlerOffset, Runtime.labelSize ()),
@@ -476,6 +478,17 @@ fun allocate {function = f: Rssa.Function.t,
                       (paramOffsets args, maxSize, fn ({offset, ty, ...}, maxSize) =>
                        Bytes.max (maxSize, Bytes.+ (offset, Type.bytes ty))))
                   val handlerOffset = Bytes.- (handlerArgsOffset, Runtime.labelSize ())
+                  val () =
+                     Control.diagnostic
+                     (fn () =>
+                      let open Layout
+                      in
+                         record
+                         [("handlerArgsOffset", Bytes.layout handlerArgsOffset),
+                          ("handlerArgsSize", Bytes.layout handlerArgsSize),
+                          ("handlerOffset", Bytes.layout handlerOffset),
+                          ("linkOffset", Bytes.layout linkOffset)]
+                      end)
                in
                   SOME {handlerArgsOffset = handlerArgsOffset,
                         handlerArgsSize = handlerArgsSize,