diff --git a/release.py b/release.py
index 6d587467..b40c3ca0 100755
--- a/release.py
+++ b/release.py
@@ -470,9 +470,13 @@ def tweak_patchlevel(
         "rc": "PY_RELEASE_LEVEL_GAMMA",
         "f": "PY_RELEASE_LEVEL_FINAL",
     }[tag.level]
-    new_constants = template.format(
-        tag=tag, level_def=level_def, plus=done and "+" or ""
-    )
+    if done:
+        # 3.15+ uses "+dev" for PEP 440 local-version compliance;
+        # 3.14 and earlier keep the bare "+" suffix.
+        plus = "+dev" if tag.as_tuple() >= (3, 15) else "+"
+    else:
+        plus = ""
+    new_constants = template.format(tag=tag, level_def=level_def, plus=plus)
     if tag.as_tuple() >= (3, 7, 0, "a", 3):
         new_constants = new_constants.expandtabs()
     constant_replace(filename, new_constants)
diff --git a/tests/test_release.py b/tests/test_release.py
index 84ee2d58..2259b1b1 100644
--- a/tests/test_release.py
+++ b/tests/test_release.py
@@ -102,6 +102,34 @@ def test_tweak_patchlevel(tmp_path: Path) -> None:
         assert expected in new_contents
 
 
+@pytest.mark.parametrize(
+    ["test_tag", "expected_py_version"],
+    [
+        # 3.14 and earlier keep the bare "+" suffix.
+        ("3.14.0b2", '#define PY_VERSION              "3.14.0b2+"'),
+        # 3.15+ uses "+dev" for PEP 440 local-version compliance.
+        ("3.15.0b1", '#define PY_VERSION              "3.15.0b1+dev"'),
+        ("3.16.0a1", '#define PY_VERSION              "3.16.0a1+dev"'),
+    ],
+)
+def test_tweak_patchlevel_done(
+    tmp_path: Path, test_tag: str, expected_py_version: str
+) -> None:
+    # Arrange
+    tag = release.Tag(test_tag)
+
+    original_patchlevel_file = Path(__file__).parent / "patchlevel.h"
+    patchlevel_file = tmp_path / "patchlevel.h"
+    patchlevel_file.write_text(original_patchlevel_file.read_text())
+
+    # Act
+    release.tweak_patchlevel(tag, filename=str(patchlevel_file), done=True)
+
+    # Assert
+    new_contents = patchlevel_file.read_text()
+    assert expected_py_version in new_contents
+
+
 @pytest.mark.parametrize(
     [
         "test_tag",