diff --git a/nominal_refactor_advisor/refactors/return_shape.py b/nominal_refactor_advisor/refactors/return_shape.py
index 12ca83b6..2cb04e15 100644
--- a/nominal_refactor_advisor/refactors/return_shape.py
+++ b/nominal_refactor_advisor/refactors/return_shape.py
@@ -30,6 +30,8 @@
 from nominal_refactor_advisor.refactors.answered_method import AnsweredMethod, AnsweredUse
 from nominal_refactor_advisor.type_checker_session import SourceTexts, TypeCheckerSession
 
+_shared_type_checker_session: TypeCheckerSession | None = None
+
 
 def _tuple_return_kind(node: ast.Return) -> str | None:
     """Classify a return statement as zero-or-one tuple, or None if other."""
@@ -179,11 +181,16 @@ def add(file_path: str, start: int, end: int, text: str) -> None:
                     add(resolved_class.file_path, start, end, new_annotation)
 
         answered = AnsweredMethod(snapshot, base, function)
-        session = TypeCheckerSession.started(SourceTexts(snapshot.parsed_modules))
+        shared = _shared_type_checker_session
+        owned_session = shared is None
+        session = shared or TypeCheckerSession.started(
+            SourceTexts(snapshot.parsed_modules)
+        )
         try:
             calls = answered.answering_calls(session)
         finally:
-            session.stop()
+            if owned_session:
+                session.stop()
 
         for use in calls:
             geo = geometry(use.file_path)