diff --git a/base/boot.jl b/base/boot.jl
index f9208c3874229..f34fb84d31ecd 100644
--- a/base/boot.jl
+++ b/base/boot.jl
@@ -1015,6 +1015,21 @@ _parse = nothing
 
 _setparser!(parser) = setglobal!(Core, :_parse, parser)
 
+
+# Binding for the julia lowerer, called as
+#
+#    Core._lower(expr, module, filename, linenum)
+#
+# Lower Julia code from the buffer `expr`, attributing
+# it to `filename`. `expr` must be the result of `_parse`
+#
+# `_lower` must return an Expr with appropriate internals to be evaled
+#
+# The internal jl_expand_with_loc_warn will call into Core._lower if not `nothing`.
+_lower = nothing
+
+_setlowerer!(lowerer) = setglobal!(Core, :_lower, lowerer)
+
 # support for deprecated uses of builtin functions
 _apply(x...) = _apply_iterate(Main.Base.iterate, x...)
 const _apply_pure = _apply
diff --git a/src/ast.c b/src/ast.c
index ab6b04efa526a..a2c68fddd22e4 100644
--- a/src/ast.c
+++ b/src/ast.c
@@ -1308,47 +1308,74 @@ JL_DLLEXPORT jl_value_t *jl_expand_with_loc_warn(jl_value_t *expr, jl_module_t *
 {
     JL_TIMING(LOWERING, LOWERING);
     jl_timing_show_location(file, line, inmodule, JL_TIMING_DEFAULT_BLOCK);
-    jl_array_t *kwargs = NULL;
-    JL_GC_PUSH2(&expr, &kwargs);
-    expr = jl_copy_ast(expr);
-    expr = jl_expand_macros(expr, inmodule, NULL, 0, ~(size_t)0, 1);
-    jl_ast_context_t *ctx = jl_ast_ctx_enter(inmodule);
-    fl_context_t *fl_ctx = &ctx->fl;
-    value_t arg = julia_to_scm(fl_ctx, expr);
-    value_t e = fl_applyn(fl_ctx, 4, symbol_value(symbol(fl_ctx, "jl-expand-to-thunk-warn")), arg,
-                          symbol(fl_ctx, file), fixnum(line), fl_ctx->F);
-    expr = scm_to_julia(fl_ctx, e, inmodule);
-    jl_ast_ctx_leave(ctx);
-    jl_sym_t *warn_sym = jl_symbol("warn");
-    if (jl_is_expr(expr) && ((jl_expr_t*)expr)->head == warn_sym) {
-        size_t nargs = jl_expr_nargs(expr);
-        for (int i = 0; i < nargs - 1; i++) {
-            jl_value_t *warning = jl_exprarg(expr, i);
-            size_t nargs = 0;
-            if (jl_is_expr(warning) && ((jl_expr_t*)warning)->head == warn_sym)
-                 nargs = jl_expr_nargs(warning);
-            int kwargs_len = (int)nargs - 6;
-            if (nargs < 6 || kwargs_len % 2 != 0) {
-                jl_error("julia-logmsg: bad argument list - expected "
-                         ":warn level (symbol) group (symbol) id file line msg . kwargs");
-            }
-            jl_value_t *level = jl_exprarg(warning, 0);
-            jl_value_t *group = jl_exprarg(warning, 1);
-            jl_value_t *id = jl_exprarg(warning, 2);
-            jl_value_t *file = jl_exprarg(warning, 3);
-            jl_value_t *line = jl_exprarg(warning, 4);
-            jl_value_t *msg = jl_exprarg(warning, 5);
-            kwargs = jl_alloc_vec_any(kwargs_len);
-            for (int i = 0; i < kwargs_len; ++i) {
-                jl_array_ptr_set(kwargs, i, jl_exprarg(warning, i + 6));
+    jl_value_t *core_lower = NULL;
+    if (jl_core_module) {
+        core_lower = jl_get_global(jl_core_module, jl_symbol("_lower"));
+    }
+    if (!core_lower || core_lower == jl_nothing) {
+        // In bootstrap, directly call the builtin lowerer.
+        jl_array_t *kwargs = NULL;
+        JL_GC_PUSH2(&expr, &kwargs);
+        expr = jl_copy_ast(expr);
+        expr = jl_expand_macros(expr, inmodule, NULL, 0, ~(size_t)0, 1);
+        jl_ast_context_t *ctx = jl_ast_ctx_enter(inmodule);
+        fl_context_t *fl_ctx = &ctx->fl;
+        value_t arg = julia_to_scm(fl_ctx, expr);
+        value_t e = fl_applyn(fl_ctx, 4, symbol_value(symbol(fl_ctx, "jl-expand-to-thunk-warn")), arg,
+                              symbol(fl_ctx, file), fixnum(line), fl_ctx->F);
+        expr = scm_to_julia(fl_ctx, e, inmodule);
+        jl_ast_ctx_leave(ctx);
+        jl_sym_t *warn_sym = jl_symbol("warn");
+        if (jl_is_expr(expr) && ((jl_expr_t*)expr)->head == warn_sym) {
+            size_t nargs = jl_expr_nargs(expr);
+            for (int i = 0; i < nargs - 1; i++) {
+                jl_value_t *warning = jl_exprarg(expr, i);
+                size_t nargs = 0;
+                if (jl_is_expr(warning) && ((jl_expr_t*)warning)->head == warn_sym)
+                     nargs = jl_expr_nargs(warning);
+                int kwargs_len = (int)nargs - 6;
+                if (nargs < 6 || kwargs_len % 2 != 0) {
+                    jl_error("julia-logmsg: bad argument list - expected "
+                             ":warn level (symbol) group (symbol) id file line msg . kwargs");
+                }
+                jl_value_t *level = jl_exprarg(warning, 0);
+                jl_value_t *group = jl_exprarg(warning, 1);
+                jl_value_t *id = jl_exprarg(warning, 2);
+                jl_value_t *file = jl_exprarg(warning, 3);
+                jl_value_t *line = jl_exprarg(warning, 4);
+                jl_value_t *msg = jl_exprarg(warning, 5);
+                kwargs = jl_alloc_vec_any(kwargs_len);
+                for (int i = 0; i < kwargs_len; ++i) {
+                    jl_array_ptr_set(kwargs, i, jl_exprarg(warning, i + 6));
+                }
+                JL_TYPECHK(logmsg, long, level);
+                jl_log(jl_unbox_long(level), NULL, group, id, file, line, (jl_value_t*)kwargs, msg);
             }
-            JL_TYPECHK(logmsg, long, level);
-            jl_log(jl_unbox_long(level), NULL, group, id, file, line, (jl_value_t*)kwargs, msg);
+            expr = jl_exprarg(expr, nargs - 1);
         }
-        expr = jl_exprarg(expr, nargs - 1);
+        JL_GC_POP();
+        return expr;
     }
+
+    jl_value_t **args;
+    JL_GC_PUSHARGS(args, 5);
+    args[0] = core_lower;
+    args[1] = expr;
+    args[2] = (jl_value_t*) inmodule;
+    jl_value_t *filename = NULL;
+    JL_GC_PUSH1(&filename);
+    filename = jl_cstr_to_string(file);
+    args[3] = filename;
     JL_GC_POP();
-    return expr;
+    args[4] = jl_box_long(line);
+    jl_task_t *ct = jl_current_task;
+    size_t last_age = ct->world_age;
+    ct->world_age = jl_atomic_load_acquire(&jl_world_counter);
+    jl_value_t *result = jl_apply(args, 5);
+    ct->world_age = last_age;
+    JL_TYPECHK(parse, expr, result);
+    JL_GC_POP();
+    return result;
 }
 
 // expand in a context where the expression value is unused
diff --git a/src/toplevel.c b/src/toplevel.c
index f1fff694926ba..21e48d904fda0 100644
--- a/src/toplevel.c
+++ b/src/toplevel.c
@@ -1128,7 +1128,7 @@ static jl_value_t *jl_parse_eval_all(jl_module_t *module, jl_value_t *text,
     ast = jl_svecref(jl_parse(jl_string_data(text), jl_string_len(text),
                               filename, 1, 0, (jl_value_t*)jl_all_sym), 0);
     if (!jl_is_expr(ast) || ((jl_expr_t*)ast)->head != jl_toplevel_sym) {
-        jl_errorf("jl_parse_all() must generate a top level expression");
+        jl_errorf("jl_parse() must generate a top level expression");
     }
 
     jl_task_t *ct = jl_current_task;
diff --git a/stdlib/InteractiveUtils/src/macros.jl b/stdlib/InteractiveUtils/src/macros.jl
index 68afc40976275..5538d79c04d1e 100644
--- a/stdlib/InteractiveUtils/src/macros.jl
+++ b/stdlib/InteractiveUtils/src/macros.jl
@@ -440,7 +440,7 @@ in the current environment.
 When using `@activate`, additional options for a component may be specified in
 square brackets `@activate Compiler[:option1, :option]`
 
-Currently `@activate Compiler` is the only available component that may be
+Currently `Compiler`, `JuliaSyntax`, and `JuliaLowering` are the only available components that may be
 activatived.
 
 For `@activate Compiler`, the following options are available:
@@ -455,6 +455,9 @@ For `@activate Compiler`, the following options are available:
 2. `:codegen`   - Activate the compiler for internal codegen purposes. The new compiler
                   will be invoked whenever the runtime requests compilation.
 
+For `@activate JuliaSyntax`, the following options are available:
+1. `:for_lowering` - Activate JuliaSyntax such that it is compatible with JuliaLowering
+
 `@activate Compiler` without options is equivalent to `@activate Compiler[:reflection]`.
 
 """
@@ -475,7 +478,7 @@ macro activate(what)
     if !isa(Component, Symbol)
         error("Usage Error: Component $Component is not a symbol")
     end
-    allowed_components = (:Compiler,)
+    allowed_components = (:Compiler, :JuliaSyntax, :JuliaLowering)
     if !(Component in allowed_components)
         error("Usage Error: Component $Component is not recognized. Expected one of $allowed_components")
     end