diff --git a/src/Lean/Compiler/LCNF/ExtractClosed.lean b/src/Lean/Compiler/LCNF/ExtractClosed.lean
index 67d4d70766..be8f79d3b2 100644
--- a/src/Lean/Compiler/LCNF/ExtractClosed.lean
+++ b/src/Lean/Compiler/LCNF/ExtractClosed.lean
@@ -13,7 +13,6 @@ public import Lean.Compiler.LCNF.ToExpr
 import Lean.Compiler.LCNF.ElimDead
 import Lean.Compiler.LCNF.DependsOn
 meta import Init.Data.FloatArray.Basic
-import Lean.Compiler.LCNF.ElimDead
 
 public section
 
diff --git a/src/Lean/Compiler/LCNF/SimpleGroundExpr.lean b/src/Lean/Compiler/LCNF/SimpleGroundExpr.lean
index cab8d65f66..800bd787a8 100644
--- a/src/Lean/Compiler/LCNF/SimpleGroundExpr.lean
+++ b/src/Lean/Compiler/LCNF/SimpleGroundExpr.lean
@@ -207,6 +207,16 @@ where
         let alignedSsize := align i.ssize 8
         let ssizeArgs := Array.replicate alignedSsize 0
         compileSetChain decl.fvarId i objArgs usizeArgs ssizeArgs k
+    | .box _ fvarId =>
+      match (← get).groundMap[fvarId]! with
+      | .uint8 v =>
+        record decl.fvarId (.arg (.tagged v.toNat))
+        go k
+      | .uint16 v =>
+        record decl.fvarId (.arg (.tagged v.toNat))
+        go k
+      -- boxed uint32/uint64 get extracted into separate closed terms automatically
+      | _ => failure
     | _ => failure
 
   compileSetChain (id : FVarId) (info : CtorInfo) (objArgs : Array SimpleGroundArg)
@@ -291,10 +301,17 @@ where
         nameAcc := .str nameAcc str
         processedArgs := processedArgs.push (ref, nameAcc.hash)
       return .nameMkStr processedArgs
-    | .pap c ys => return .pap c (← compileArgs ys)
     | .fap c #[] =>
       guard <| isSimpleGroundDecl (← getEnv) c
       return .reference c
+    | .box _ fvarId =>
+      match (← get).groundMap[fvarId]! with
+      | .uint32 _ => failure -- TODO: figure out how to do this properly with 32/64bit restrictions
+      | .uint64 v => return .ctor 0 #[] #[] (uint64ToByteArrayLE v)
+      | .usize v => return .ctor 0 #[] #[v] #[]
+      | .uint8 _ | .uint16 _ -- boxed uint8/uint16 should never be final expressions
+      | _ => failure
+    | .pap c ys => return .pap c (← compileArgs ys)
     | _ => failure
 
   compileArg (arg : Arg .impure) : DetectM SimpleGroundArg := do
diff --git a/tests/elab/simple_ground_extraction.lean b/tests/elab/simple_ground_extraction.lean
index ff0b5f9ed5..d8e789b722 100644
--- a/tests/elab/simple_ground_extraction.lean
+++ b/tests/elab/simple_ground_extraction.lean
@@ -496,3 +496,113 @@ trace: [Compiler.simpleGround] Marked testWithUSizeAndScalars._closed_0 as simpl
 set_option trace.Compiler.saveImpure true in
 set_option trace.Compiler.simpleGround true in
 def testWithUSizeAndScalars : WithUSizeAndScalars := ⟨"WUAS", 0, 1, 2, 3, 4⟩
+
+
+/--
+trace: [Compiler.simpleGround] Marked uint8Pair._closed_0 as simple ground expr
+[Compiler.simpleGround] Marked uint8Pair as simple ground expr
+[Compiler.saveImpure] size: 5
+    def uint8Pair._closed_0 : obj :=
+      let _x.1 := 3;
+      let _x.2 := 1;
+      let _x.3 := box _x.2;
+      let _x.4 := box _x.1;
+      let _x.5 := ctor_0[Prod.mk] _x.3 _x.4;
+      return _x.5
+[Compiler.saveImpure] size: 1
+    def uint8Pair : obj :=
+      let _x.1 := uint8Pair._closed_0;
+      return _x.1
+-/
+#guard_msgs in
+set_option trace.Compiler.saveImpure true in
+set_option trace.Compiler.simpleGround true in
+def uint8Pair : UInt8 × UInt8 := (1,3)
+
+
+/--
+trace: [Compiler.simpleGround] Marked uint16Pair._closed_0 as simple ground expr
+[Compiler.simpleGround] Marked uint16Pair as simple ground expr
+[Compiler.saveImpure] size: 5
+    def uint16Pair._closed_0 : obj :=
+      let _x.1 := 3;
+      let _x.2 := 1;
+      let _x.3 := box _x.2;
+      let _x.4 := box _x.1;
+      let _x.5 := ctor_0[Prod.mk] _x.3 _x.4;
+      return _x.5
+[Compiler.saveImpure] size: 1
+    def uint16Pair : obj :=
+      let _x.1 := uint16Pair._closed_0;
+      return _x.1
+-/
+#guard_msgs in
+set_option trace.Compiler.saveImpure true in
+set_option trace.Compiler.simpleGround true in
+def uint16Pair : UInt16 × UInt16 := (1,3)
+
+-- TODO: UInt32 support
+
+
+/--
+trace: [Compiler.simpleGround] Marked uint64Pair._closed_0._boxed_const_1 as simple ground expr
+[Compiler.simpleGround] Marked uint64Pair._closed_0._boxed_const_2 as simple ground expr
+[Compiler.simpleGround] Marked uint64Pair._closed_0 as simple ground expr
+[Compiler.simpleGround] Marked uint64Pair as simple ground expr
+[Compiler.saveImpure] size: 2
+    def uint64Pair._closed_0._boxed_const_1 : tobj :=
+      let _x.1 := 1;
+      let _x.2 := box _x.1;
+      return _x.2
+[Compiler.saveImpure] size: 2
+    def uint64Pair._closed_0._boxed_const_2 : tobj :=
+      let _x.1 := 3;
+      let _x.2 := box _x.1;
+      return _x.2
+[Compiler.saveImpure] size: 3
+    def uint64Pair._closed_0 : obj :=
+      let _x.1 := uint64Pair._closed_0._boxed_const_1;
+      let _x.2 := uint64Pair._closed_0._boxed_const_2;
+      let _x.3 := ctor_0[Prod.mk] _x.1 _x.2;
+      return _x.3
+[Compiler.saveImpure] size: 1
+    def uint64Pair : obj :=
+      let _x.1 := uint64Pair._closed_0;
+      return _x.1
+-/
+#guard_msgs in
+set_option trace.Compiler.saveImpure true in
+set_option trace.Compiler.simpleGround true in
+def uint64Pair : UInt64 × UInt64 := (1,3)
+
+
+/--
+trace: [Compiler.simpleGround] Marked usizePair._closed_0._boxed_const_1 as simple ground expr
+[Compiler.simpleGround] Marked usizePair._closed_0._boxed_const_2 as simple ground expr
+[Compiler.simpleGround] Marked usizePair._closed_0 as simple ground expr
+[Compiler.simpleGround] Marked usizePair as simple ground expr
+[Compiler.saveImpure] size: 2
+    def usizePair._closed_0._boxed_const_1 : tobj :=
+      let _x.1 := 1;
+      let _x.2 := box _x.1;
+      return _x.2
+[Compiler.saveImpure] size: 2
+    def usizePair._closed_0._boxed_const_2 : tobj :=
+      let _x.1 := 3;
+      let _x.2 := box _x.1;
+      return _x.2
+[Compiler.saveImpure] size: 3
+    def usizePair._closed_0 : obj :=
+      let _x.1 := usizePair._closed_0._boxed_const_1;
+      let _x.2 := usizePair._closed_0._boxed_const_2;
+      let _x.3 := ctor_0[Prod.mk] _x.1 _x.2;
+      return _x.3
+[Compiler.saveImpure] size: 1
+    def usizePair : obj :=
+      let _x.1 := usizePair._closed_0;
+      return _x.1
+-/
+#guard_msgs in
+set_option trace.Compiler.saveImpure true in
+set_option trace.Compiler.simpleGround true in
+def usizePair : USize × USize := (1,3)