@@ -15,7 +15,7 @@ would perhaps a better fit.
 
     >>> v = Version.parse("3.4.5-pre.2+build.4")
     >>> str(v.next_version(part="prerelease"))
-    '3.4.5-pre.3'
+    '3.4.5-rc.1'
     >>> str(Version.parse("3.4.5-pre.2+build.4").next_version(part="patch"))
     '3.4.5'
     >>> str(Version.parse("3.4.5+build.4").next_version(part="patch"))
 
@@ -482,6 +482,10 @@ 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:
+                current_token = version.prerelease.split(".")[0]
+                if current_token != prerelease_token:
+                    return version.replace(prerelease=f"{prerelease_token}.1", build=None)
             return version.bump_prerelease(prerelease_token, bump_when_empty=True)
 
     @_comparator