pabszero · Oct 19, 2026 · Oct 19, 2026 · Oct 19, 2026
diff --git a/changelog.d/499.bugfix.rst b/changelog.d/499.bugfix.rst
@@ -0,0 +1,5 @@
+``Version.next_version("prerelease")`` now advances the patch version when
+incrementing an old-style prerelease counter would produce an older version.
+For example, ``1.2.3-rc9`` becomes ``1.2.4-rc10``. The legacy token and
+incremented counter are preserved; increments that already move forward keep
+the current patch version.
diff --git a/src/semver/version.py b/src/semver/version.py
@@ -524,6 +524,12 @@ def next_version(self, part: str, prerelease_token: str = "rc") -> "Version":
         >>> str(semver.Version.parse("1.2.3-rc.1").next_version("prerelease", "alpha"))
         '1.2.4-alpha.1'
 
+        Old-style counters also advance the patch version if incrementing
+        the counter would move backwards under SemVer's lexical ordering:
+
+        >>> str(semver.Version.parse("1.2.3-rc9").next_version("prerelease"))
+        '1.2.4-rc10'
+
         :param part: One of "major", "minor", "patch", or "prerelease"
         :param prerelease_token: prefix string of prerelease, defaults to 'rc'
         :return: new object with the appropriate part raised
@@ -560,9 +566,14 @@ def next_version(self, part: str, prerelease_token: str = "rc") -> "Version":
                 )
                 if match:
                     num = int(match.group(1))
-                    return version.replace(
+                    candidate = version.replace(
                         prerelease=f"{prerelease_token}{num + 1}", build=None
                     )
+                    if candidate > version:
+                        return candidate
+                    return candidate.bump_patch().replace(
+                        prerelease=candidate.prerelease
+                    )
 
                 if not (
                     version.prerelease == prerelease_token

diff --git a/tests/test_issue484.py b/tests/test_issue484.py
@@ -31,9 +31,11 @@ def test_issue_484_rc3_to_rc4():
 
 
 def test_issue_484_rc9_to_rc10():
-    """Ensure numeric bumping works across digit boundaries."""
+    """Keep the legacy counter while ensuring digit rollover moves forward."""
     v = Version.parse("1.2.3-rc9")
-    assert str(v.next_version("prerelease")) == "1.2.3-rc10"
+    result = v.next_version("prerelease")
+    assert str(result) == "1.2.4-rc10"
+    assert result > v
 
 
 def test_issue_484_dot_style_unchanged():

diff --git a/tests/test_next_version_legacy_order.py b/tests/test_next_version_legacy_order.py
@@ -0,0 +1,46 @@
+"""Legacy prerelease counters must not make next_version move backwards."""
+
+import pytest
+
+from semver import Version
+
+
+@pytest.mark.parametrize(
+    "current,token,expected",
+    [
+        ("1.2.3-rc9", "rc", "1.2.4-rc10"),
+        ("1.2.3-rc99", "rc", "1.2.4-rc100"),
+        ("1.2.3-rc999+build.7", "rc", "1.2.4-rc1000"),
+        ("1.2.3-beta9", "beta", "1.2.4-beta10"),
+        ("1.2.3-alpha.beta9", "alpha.beta", "1.2.4-alpha.beta10"),
+        ("1.2.3-0rc9", "0rc", "1.2.4-0rc10"),
+        ("0.0.0-rc9", "rc", "0.0.1-rc10"),
+        ("1.2.3-rc8", "rc", "1.2.3-rc9"),
+        ("1.2.3-rc98", "rc", "1.2.3-rc99"),
+        ("1.2.3-rc099", "rc", "1.2.3-rc100"),
+        ("1.2.3-rc09", "rc", "1.2.3-rc10"),
+        ("1.2.3-rc.9", "rc", "1.2.3-rc.10"),
+    ],
+)
+def test_next_legacy_counter_preserves_order(current, token, expected):
+    original = Version.parse(current)
+    result = original.next_version("prerelease", token)
+    assert str(result) == expected
+    assert result > original
+    assert result.build is None
+    assert Version.parse(str(result)).to_tuple() == result.to_tuple()
+    assert str(original) == current
+
+
+def test_repeated_legacy_bumps_preserve_order_and_subclass():
+    class Release(Version):
+        pass
+
+    current = Release.parse("1.2.3-rc8+build.7")
+    for expected in ("1.2.3-rc9", "1.2.4-rc10", "1.2.4-rc11"):
+        result = current.next_version("prerelease")
+        assert isinstance(result, Release)
+        assert str(result) == expected
+        assert result > current
+        assert result.build is None
+        current = result