diff --git a/src/codeedges.jl b/src/codeedges.jl
index 00a727b..10181c8 100644
--- a/src/codeedges.jl
+++ b/src/codeedges.jl
@@ -793,10 +793,10 @@ end
 #
 # [Wei84]: M. Weiser, "Program Slicing," IEEE Transactions on Software Engineering, 10, pages 352-357, July 1984.
 function add_control_flow!(isrequired, src::CodeInfo, cfg::CFG, postdomtree)
-    local changed::Bool = false
+    changed = Ref(false)
     function mark_isrequired!(idx::Int)
         if !isrequired[idx]
-            changed |= isrequired[idx] = true
+            changed[] |= isrequired[idx] = true
             return true
         end
         return false
@@ -818,7 +818,7 @@ function add_control_flow!(isrequired, src::CodeInfo, cfg::CFG, postdomtree)
             end
         end
     end
-    return changed
+    return changed[]
 end
 
 is_conditional_terminator(@nospecialize stmt) = stmt isa GotoIfNot ||
diff --git a/test/runtests.jl b/test/runtests.jl
index 9721a39..7b55c24 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1,10 +1,14 @@
-using Test
+using Test, LoweredCodeUtils
 
 # using LoweredCodeUtils
 # @testset "Ambiguity" begin
 #     @test isempty(detect_ambiguities(LoweredCodeUtils, LoweredCodeUtils.JuliaInterpreter, Base, Core))
 # end
 
+if isdefined(Test, :detect_closure_boxes)
+    @test isempty(Test.detect_closure_boxes(LoweredCodeUtils))
+end
+
 @testset "LoweredCodeUtils.jl" begin
     @testset "signatures.jl" include("signatures.jl")
     @testset "codeedges.jl" include("codeedges.jl")