diff --git a/src/ast.jl b/src/ast.jl
index a7b087c..93f5a7c 100644
--- a/src/ast.jl
+++ b/src/ast.jl
@@ -70,6 +70,21 @@ Id for scope layers in macro expansion
 """
 const LayerId = Int
 
+"""
+A `ScopeLayer` is a mechanism for automatic hygienic macros; every identifier
+is assigned to a particular layer and can only match against bindings which are
+themselves part of that layer.
+
+Normal code contains a single scope layer, whereas each macro expansion
+generates a new layer.
+"""
+struct ScopeLayer
+    id::LayerId
+    mod::Module
+    parent_layer::LayerId # Index of parent layer in a macro expansion. Equal to 0 for no parent
+    is_macro_expansion::Bool # FIXME
+end
+
 #-------------------------------------------------------------------------------
 # AST creation utilities
 _node_id(graph::SyntaxGraph, ex::SyntaxTree) = (check_compatible_graph(graph, ex); ex._id)
@@ -500,6 +515,10 @@ function adopt_scope(ex::SyntaxTree, scope_layer::LayerId)
     set_scope_layer(ex, ex, scope_layer, true)
 end
 
+function adopt_scope(ex::SyntaxTree, layer::ScopeLayer)
+    adopt_scope(ex, layer.id)
+end
+
 function adopt_scope(ex::SyntaxTree, ref::SyntaxTree)
     adopt_scope(ex, ref.scope_layer)
 end
diff --git a/src/macro_expansion.jl b/src/macro_expansion.jl
index 84efb44..d48cb13 100644
--- a/src/macro_expansion.jl
+++ b/src/macro_expansion.jl
@@ -1,20 +1,5 @@
 # Lowering pass 1: Macro expansion, simple normalizations and quote expansion
 
-"""
-A `ScopeLayer` is a mechanism for automatic hygienic macros; every identifier
-is assigned to a particular layer and can only match against bindings which are
-themselves part of that layer.
-
-Normal code contains a single scope layer, whereas each macro expansion
-generates a new layer.
-"""
-struct ScopeLayer
-    id::LayerId
-    mod::Module
-    parent_layer::LayerId # Index of parent layer in a macro expansion. Equal to 0 for no parent
-    is_macro_expansion::Bool # FIXME
-end
-
 struct MacroExpansionContext{GraphType} <: AbstractLoweringContext
     graph::GraphType
     bindings::Bindings
diff --git a/src/runtime.jl b/src/runtime.jl
index e6b03ce..e7bd83c 100644
--- a/src/runtime.jl
+++ b/src/runtime.jl
@@ -343,9 +343,11 @@ function (g::GeneratedFunctionStub)(world::UInt, source::Method, @nospecialize a
     macro_world = typemax(UInt)
     ctx1 = MacroExpansionContext(graph, __module__, false, macro_world)
 
+    layer = only(ctx1.scope_layers)
+
     # Run code generator - this acts like a macro expander and like a macro
     # expander it gets a MacroContext.
-    mctx = MacroContext(syntax_graph(ctx1), g.srcref, ctx1.scope_layers[end])
+    mctx = MacroContext(syntax_graph(ctx1), g.srcref, layer)
     ex0 = g.gen(mctx, args...)
     if ex0 isa SyntaxTree
         if !is_compatible_graph(ctx1, ex0)
@@ -370,10 +372,10 @@ function (g::GeneratedFunctionStub)(world::UInt, source::Method, @nospecialize a
     # Wrap expansion in a non-toplevel lambda and run scope resolution
     ex2 = @ast ctx2 ex0 [K"lambda"(is_toplevel_thunk=false, toplevel_pure=true)
         [K"block"
-            (string(n)::K"Identifier" for n in g.argnames)...
+            (adopt_scope(string(n)::K"Identifier", layer) for n in g.argnames)...
         ]
         [K"block"
-            (string(n)::K"Identifier" for n in g.spnames)...
+            (adopt_scope(string(n)::K"Identifier", layer) for n in g.spnames)...
         ]
         ex2
     ]
diff --git a/src/scope_analysis.jl b/src/scope_analysis.jl
index 4d751a8..ce3f0fb 100644
--- a/src/scope_analysis.jl
+++ b/src/scope_analysis.jl
@@ -12,16 +12,9 @@ function Base.isless(a::NameKey, b::NameKey)
     (a.name, a.layer) < (b.name, b.layer)
 end
 
-# Identifiers produced by lowering will have the following layer by default.
-#
-# To make new mutable variables without colliding names, lowering can
-# - generate new var_id's directly (like the gensyms used by the old system)
-# - create additional layers, though this may be unnecessary
-const _lowering_internal_layer = -1
-
 function NameKey(ex::SyntaxTree)
     @chk kind(ex) == K"Identifier"
-    NameKey(ex.name_val, get(ex, :scope_layer, _lowering_internal_layer))
+    NameKey(ex.name_val, ex.scope_layer)
 end
 
 #-------------------------------------------------------------------------------