diff --git a/src/protocol/ast_printer.rs b/src/protocol/ast_printer.rs
index 22a5db0376dda2d918d174df982d37d19cec4970..6411ae43cdff50018a3480bfe57184099ff812aa 100644
--- a/src/protocol/ast_printer.rs
+++ b/src/protocol/ast_printer.rs
@@ -770,7 +770,7 @@ impl ASTWriter {
                 self.kv(indent2).with_s_key("Method").with_debug_val(&expr.method);
                 if !expr.procedure.is_invalid() {
                     let definition = &heap[expr.procedure];
-                    self.kv(indent2).with_s_key("BuiltIn").with_disp_val(&definition.builtin);
+                    self.kv(indent2).with_s_key("Source").with_debug_val(&definition.source);
                     self.kv(indent2).with_s_key("Variant").with_debug_val(&definition.kind);
                     self.kv(indent2).with_s_key("MethodName").with_identifier_val(&definition.identifier);
                     self.kv(indent2).with_s_key("ParserType")