diff --git a/docs/python-pyc.md b/docs/python-pyc.md
index c2674a8cce..33942187fa 100644
--- a/docs/python-pyc.md
+++ b/docs/python-pyc.md
@@ -50,7 +50,9 @@ names, locals (or `localsplusnames` on 3.11+), const
 summaries, and bytecode length plus SHA-256.
 
 Code-object equality used by sets and dictionaries follows the selected layout:
-3.7–3.10 ignore line tables, while 3.11+ include line and exception tables. The
+3.7–3.10 derive `CO_NOFREE` from the free/cell tables for equality, while
+3.11+ compare raw flags; raw `co_flags` remain in reported facts. The older
+layouts ignore line tables, while 3.11+ include line and exception tables. The
 artifact SHA-256 identifies the exact selected `.pyc` bytes independently of
 this decoded object graph. Reference slots follow each tag's CPython behavior:
 singleton values and `TYPE_REF` do not reserve new slots even when their tag
diff --git a/src/python/PythonPycParser.ts b/src/python/PythonPycParser.ts
index 6698323ace..f27a9d1819 100644
--- a/src/python/PythonPycParser.ts
+++ b/src/python/PythonPycParser.ts
@@ -56,6 +56,8 @@ const TYPES_WITHOUT_REFERENCE_SLOTS = new Set([
 /** CPython `CO_VARARGS` / `CO_VARKEYWORDS`. Each consumes one local name. */
 const CO_VARARGS = 0x04;
 const CO_VARKEYWORDS = 0x08;
+/** CPython 3.7–3.10 derives this bit from the free/cell variable tables. */
+const CO_NOFREE = 0x40;
 /** CPython `_PyLocals_Kind` bit counted by `_PyCode_Validate` as a local. */
 const CO_FAST_LOCAL = 0x20;
 
@@ -149,6 +151,7 @@ const containerChildren = (value: MarshalValue): readonly MarshalValue[] => {
  */
 type CodeEquality = {
   readonly consts: readonly MarshalValue[];
+  readonly effectiveFlags: number;
   readonly linetable: string;
   readonly exceptiontable: string;
 };
@@ -520,8 +523,15 @@ class MarshalReader {
       consts: [],
       nested: [],
     };
+    const effectiveFlags =
+      this.layout === "py311"
+        ? flags
+        : (freevars?.length ?? 0) === 0 && (cellvars?.length ?? 0) === 0
+          ? flags | CO_NOFREE
+          : flags & ~CO_NOFREE;
     this.#codeEquality.set(node, {
       consts,
+      effectiveFlags,
       linetable: `${linetable.length}:${sha256(linetable)}`,
       exceptiontable: `${exceptiontable.length}:${sha256(exceptiontable)}`,
     });
@@ -1176,7 +1186,7 @@ class MarshalReader {
       String(node.posonlyargcount ?? 0),
       String(node.kwonlyargcount),
       node.nlocals === null ? "" : String(node.nlocals),
-      String(node.flags),
+      String(material.effectiveFlags),
       String(node.firstlineno),
       `${node.bytecode.bytes}:${node.bytecode.sha256}`,
       this.#constKeyItems(material.consts),
diff --git a/tests/acceptance/pythonPycCli.test.ts b/tests/acceptance/pythonPycCli.test.ts
index 352d1a9fb8..ef55f2b98b 100644
--- a/tests/acceptance/pythonPycCli.test.ts
+++ b/tests/acceptance/pythonPycCli.test.ts
@@ -298,6 +298,116 @@ cliTest(
   },
 );
 
+cliTest(
+  "uses constructor-normalized legacy flags for code keys and preserves raw flags",
+  async ({ cli }) => {
+    const root = await createTestTempDirectory(
+      "rea-python-pyc-effective-flags-",
+    );
+    const cases = [
+      {
+        name: "py37-empty-tables",
+        magic: 3394,
+        layout: "py37" as const,
+        freevars: [],
+        cellvars: [],
+        lengths: [1, 1],
+      },
+      {
+        name: "py310-nonempty-tables",
+        magic: 3439,
+        layout: "py38" as const,
+        freevars: ["capture"],
+        cellvars: [],
+        lengths: [1, 1],
+      },
+      {
+        name: "py311-raw-flags",
+        magic: 3531,
+        layout: "py311" as const,
+        freevars: [],
+        cellvars: [],
+        lengths: [2, 2],
+      },
+    ];
+    for (const testCase of cases) {
+      const code = (flags: number) =>
+        marshalCode(testCase.layout, {
+          name: "f",
+          filename: "fixture.py",
+          firstlineno: 1,
+          flags,
+          freevars: testCase.freevars,
+          cellvars: testCase.cellvars,
+        });
+      const first = code(0);
+      const second = code(0x40);
+      const frozenSet = Buffer.concat([
+        Buffer.from([0x3e]),
+        Buffer.from([2, 0, 0, 0]),
+        first,
+        second,
+      ]);
+      const dict = Buffer.concat([
+        Buffer.from([0x7b]),
+        first,
+        Buffer.from([0x4e]),
+        second,
+        Buffer.from([0x54, 0x30]),
+      ]);
+      const path = join(root, `${testCase.name}.pyc`);
+      await writeFile(
+        path,
+        Buffer.concat([
+          pythonPycHeader(testCase.magic),
+          marshalCode(testCase.layout, { consts: [frozenSet, dict] }),
+        ]),
+      );
+      const result = await cli.run({
+        arguments: ["inspect-python-pyc", path, "--json"],
+      });
+      expect(result.exitCode, result.stderr).toBe(0);
+      const evidence = toolContract("inspect_python_pyc").outputSchema.parse(
+        result.json,
+      );
+      expect(
+        evidence.normalized_result.code_objects[0]?.consts.map((value) =>
+          value.kind === "frozenset" || value.kind === "dict"
+            ? value.length
+            : null,
+        ),
+      ).toEqual(testCase.lengths);
+      expect(
+        evidence.normalized_result.code_objects
+          .filter((object) => object.name === "f")
+          .map((object) => object.flags),
+      ).toContain(0);
+
+      const rawPath = join(root, `raw-${testCase.name}.pyc`);
+      await writeFile(
+        rawPath,
+        Buffer.concat([
+          pythonPycHeader(testCase.magic),
+          marshalCode(testCase.layout, {
+            name: "f",
+            flags: 0x40,
+            freevars: testCase.freevars,
+            cellvars: testCase.cellvars,
+          }),
+        ]),
+      );
+      const rawResult = await cli.run({
+        arguments: ["inspect-python-pyc", rawPath, "--json"],
+      });
+      expect(rawResult.exitCode, rawResult.stderr).toBe(0);
+      const rawEvidence = toolContract("inspect_python_pyc").outputSchema.parse(
+        rawResult.json,
+      );
+      expect(rawEvidence.normalized_result.code_objects[0]?.flags).toBe(0x40);
+    }
+  },
+);
+
 cliTest(
   "resolves a relative pyc path against the working directory",
   async ({ cli }) => {