diff --git a/.github/workflows/python-app.yml b/.github/workflows/python-app.yml
index bda57a97..51707ce7 100644
--- a/.github/workflows/python-app.yml
+++ b/.github/workflows/python-app.yml
@@ -16,13 +16,17 @@ jobs:
   build:
 
     runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        python-version: ["3.9", "3.13"]
 
     steps:
     - uses: actions/checkout@v4
-    - name: Set up Python 3.9
+    - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v3
       with:
-        python-version: "3.9"
+        python-version: ${{ matrix.python-version }}
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
diff --git a/opto/trace/bundle.py b/opto/trace/bundle.py
index 57b9901a..66c30309 100644
--- a/opto/trace/bundle.py
+++ b/opto/trace/bundle.py
@@ -51,7 +51,9 @@ def bundle(
     Returns:
         FunModule: The wrapped function that returns node objects.
     """
-    prev_f_locals = inspect.stack()[1].frame.f_locals
+    # Python 3.13+ returns a live FrameLocalsProxy here rather than a dict (PEP 667);
+    # snapshot it so the captured locals stay a plain dict on every version.
+    prev_f_locals = dict(inspect.stack()[1].frame.f_locals)
 
     def decorator(fun):
         fun_module = FunModule(
diff --git a/tests/unit_tests/test_bundle.py b/tests/unit_tests/test_bundle.py
index ea00c6d3..4a37575f 100644
--- a/tests/unit_tests/test_bundle.py
+++ b/tests/unit_tests/test_bundle.py
@@ -425,4 +425,22 @@ def modify_global_list():
 print("Running tests with trainable=False")
 run(trainable=False)
 print("Running tests with trainable=True")
-run(trainable=True)
\ No newline at end of file
+run(trainable=True)
+
+def test_caller_locals_are_captured_as_dict():
+    # Regression test for #43. bundle() captures the calling frame's locals so a
+    # trainable operator can be re-executed with them. On Python 3.13+ frame.f_locals
+    # is a live FrameLocalsProxy rather than a dict (PEP 667), which used to trip the
+    # isinstance check in FunModule and made bundle unusable on 3.13.
+    nonlocal_marker = node("This is a nonlocal marker")
+
+    @trace.bundle()
+    def uses_marker(x):
+        return x
+
+    assert isinstance(uses_marker._ldict, dict)
+    assert uses_marker._ldict["nonlocal_marker"] is nonlocal_marker
+
+
+print("Running caller-locals capture test")
+test_caller_locals_are_captured_as_dict()