@@ -0,0 +1 @@
+Fix :meth:`~semver.Version.next_version` to correctly increment old-style prerelease versions without a dot separator (for example ``rc3``). Previously, calling ``next_version("prerelease")`` on such versions would reset the prerelease number to 1 instead of incrementing it.
@@ -539,7 +539,13 @@ def next_version(self, part: str, prerelease_token: str = "rc") -> "Version":
         if part in cls.NAMES[:3]:
             return getattr(version, "bump_" + part)()
         else:
-            if version.prerelease is not None and prerelease_token:
+            if version.prerelease and prerelease_token:
+                # Handle old-style prereleases like "rc3" (no dot separator)
+                match = re.match(f"^{prerelease_token}(\\d+)$", version.prerelease)
+                if match:
+                    num = int(match.group(1))
+                    return version.replace(prerelease=f"{prerelease_token}{num + 1}")
+
                 current_token = version.prerelease.split(".")[0]
                 if current_token != prerelease_token:
                     return version.replace(prerelease=f"{prerelease_token}.1", build=None)
 
@@ -0,0 +1,33 @@
+"""Regression test for issue #484: next_version with old-style prereleases."""
+
+from semver import Version
+
+
+def test_issue_484_rc3_to_rc4():
+    """Old-style prerelease 'rc3' should bump to 'rc4', not reset to 'rc.1'."""
+    v = Version.parse("0.1.2-rc3")
+    assert str(v.next_version("prerelease")) == "0.1.2-rc4"
+
+
+def test_issue_484_rc9_to_rc10():
+    """Ensure numeric bumping works across digit boundaries."""
+    v = Version.parse("1.2.3-rc9")
+    assert str(v.next_version("prerelease")) == "1.2.3-rc10"
+
+
+def test_issue_484_dot_style_unchanged():
+    """Dot-separated prereleases should still work as before."""
+    v = Version.parse("0.1.2-rc.3")
+    assert str(v.next_version("prerelease")) == "0.1.2-rc.4"
+
+
+def test_issue_484_different_token():
+    """A different prerelease token should still reset to rc.1."""
+    v = Version.parse("1.2.3-alpha1")
+    assert str(v.next_version("prerelease")) == "1.2.3-rc.1"
+
+
+def test_issue_484_custom_token():
+    """Custom prerelease token should be respected."""
+    v = Version.parse("1.2.3-beta2")
+    assert str(v.next_version("prerelease", "beta")) == "1.2.3-beta3"
Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	+Fix :meth:`~semver.Version.next_version` to correctly increment old-style prerelease versions without a dot separator (for example ``rc3``). Previously, calling ``next_version("prerelease")`` on such versions would reset the prerelease number to 1 instead of incrementing it.