diff --git a/docs/release-notes/.FSharp.Compiler.Service/11.0.100.md b/docs/release-notes/.FSharp.Compiler.Service/11.0.100.md
index ab65df29a6e..879be45c437 100644
--- a/docs/release-notes/.FSharp.Compiler.Service/11.0.100.md
+++ b/docs/release-notes/.FSharp.Compiler.Service/11.0.100.md
@@ -130,6 +130,7 @@
 * Fix dot-completion after indexed expressions (`a.[0].Data.`, `a[0].Data.`, `[1;2].Length.`) returning unrelated global completions instead of expression-typings members. ([Issue #4966](https://github.com/dotnet/fsharp/issues/4966), [PR #19934](https://github.com/dotnet/fsharp/pull/19934))
 * Quotations of `match s with "" -> _` no longer leak the `s <> null && s.Length = 0` lowering; the empty-string optimization moved from pattern-match compilation to the optimizer so quoted expressions keep `op_Equality(s, "")`. ([Issue #19873](https://github.com/dotnet/fsharp/issues/19873))
 * Fix #5795: Allow attributes defined in a `module rec` / `namespace rec` scope to be used on union cases, record fields, and generic type parameters of types in the same recursive scope. ([Issue #5795](https://github.com/dotnet/fsharp/issues/5795), [PR #19744](https://github.com/dotnet/fsharp/pull/19744))
+* Avoid per-instance lock object in InterruptibleLazy and DelayInitArrayMap (PR [#20088](https://github.com/dotnet/fsharp/pull/20088))
 
 ### Added
 
diff --git a/src/Compiler/Utilities/illib.fs b/src/Compiler/Utilities/illib.fs
index 87434b07720..0b8d51be0a3 100644
--- a/src/Compiler/Utilities/illib.fs
+++ b/src/Compiler/Utilities/illib.fs
@@ -15,8 +15,6 @@ open FSharp.Compiler.Caches
 
 [<Class>]
 type InterruptibleLazy<'T> private (value, valueFactory: unit -> 'T) =
-    let syncObj = obj ()
-
     [<VolatileField>]
     // TODO nullness - this is boxed to obj because of an attribute targets bug fixed in main, but not yet shipped (needs shipped 8.0.400)
     let mutable valueFactory: objnull = valueFactory
@@ -34,7 +32,7 @@ type InterruptibleLazy<'T> private (value, valueFactory: unit -> 'T) =
         match valueFactory with
         | null -> value
         | _ ->
-            Monitor.Enter(syncObj)
+            Monitor.Enter(this)
 
             try
                 match valueFactory with
@@ -44,7 +42,7 @@ type InterruptibleLazy<'T> private (value, valueFactory: unit -> 'T) =
                     value <- (valueFactory |> unbox<unit -> 'T>) ()
                     valueFactory <- Unchecked.defaultof<_>
             finally
-                Monitor.Exit(syncObj)
+                Monitor.Exit(this)
 
             value
 
@@ -151,8 +149,6 @@ module internal PervasiveAutoOpens =
 
 [<AbstractClass>]
 type DelayInitArrayMap<'T, 'TDictKey, 'TDictValue>(f: unit -> 'T[]) =
-    let syncObj = obj ()
-
     let mutable arrayStore: (_ array | null) = null
     let mutable dictStore: (_ | null) = null
 
@@ -162,7 +158,7 @@ type DelayInitArrayMap<'T, 'TDictKey, 'TDictValue>(f: unit -> 'T[]) =
         match arrayStore with
         | NonNull value -> value
         | _ ->
-            Monitor.Enter(syncObj)
+            Monitor.Enter(this)
 
             try
                 match arrayStore with
@@ -174,14 +170,14 @@ type DelayInitArrayMap<'T, 'TDictKey, 'TDictValue>(f: unit -> 'T[]) =
                     func <- Unchecked.defaultof<_>
                     freshArray
             finally
-                Monitor.Exit(syncObj)
+                Monitor.Exit(this)
 
     member this.GetDictionary() =
         match dictStore with
         | NonNull value -> value
         | _ ->
             let array = this.GetArray()
-            Monitor.Enter(syncObj)
+            Monitor.Enter(this)
 
             try
                 match dictStore with
@@ -191,7 +187,7 @@ type DelayInitArrayMap<'T, 'TDictKey, 'TDictValue>(f: unit -> 'T[]) =
                     dictStore <- dict
                     dict
             finally
-                Monitor.Exit(syncObj)
+                Monitor.Exit(this)
 
     abstract CreateDictionary: 'T[] -> IDictionary<'TDictKey, 'TDictValue>