diff --git a/docs/changes.rst b/docs/changes.rst
index d99ae92e6640..7b3576fd3b73 100644
--- a/docs/changes.rst
+++ b/docs/changes.rst
@@ -9,6 +9,8 @@ Not yet released.
 
 **Bug fixes**
 
+* Update outdated plural definitions during the database migration.
+
 **Compatibility**
 
 **Upgrading**
diff --git a/pyproject.toml b/pyproject.toml
index 43e90eac38be..9a7bd7fa4746 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -84,7 +84,7 @@ dependencies = [
   "translate-toolkit>=3.14.1,<3.15",
   "translation-finder>=2.16,<3.0",
   "user-agents>=2.0,<2.3",
-  "weblate-language-data>=2024.6",
+  "weblate-language-data>=2024.9",
   "weblate-schemas==2024.1"
 ]
 description = "A web-based continuous localization system with tight version control integration"
diff --git a/weblate/lang/models.py b/weblate/lang/models.py
index 3ff5eb5fb93a..4d57f5400db6 100644
--- a/weblate/lang/models.py
+++ b/weblate/lang/models.py
@@ -30,6 +30,7 @@
 from weblate.checks.format import BaseFormatCheck
 from weblate.checks.models import CHECKS
 from weblate.lang import data
+from weblate.lang.data import FORMULA_WITH_ZERO
 from weblate.logger import LOGGER
 from weblate.trans.defines import LANGUAGE_CODE_LENGTH, LANGUAGE_NAME_LENGTH
 from weblate.trans.mixins import CacheKeyMixin
@@ -460,7 +461,7 @@ def default_language(self):
         """Return English language object."""
         return self.get(code=settings.DEFAULT_LANGUAGE, skip_cache=True)
 
-    def setup(self, update, logger=lambda x: x) -> None:
+    def setup(self, update, logger=lambda x: x) -> None:  # noqa: C901
         """
         Create basic set of languages.
 
@@ -472,7 +473,7 @@ def setup(self, update, logger=lambda x: x) -> None:
         # Invalidate cache, we might change languages
         self.flush_object_cache()
         languages = {language.code: language for language in self.prefetch()}
-        plurals: dict[str, dict[int, list[str]]] = {}
+        plurals: dict[str, dict[int, list[Plural]]] = {}
         # Create Weblate languages
         for code, name, nplurals, plural_formula in LANGUAGES:
             population = POPULATION[code]
@@ -555,8 +556,35 @@ def setup(self, update, logger=lambda x: x) -> None:
                         formula=plural_formula,
                         type=get_plural_type(lang.base_code, plural_formula),
                     )
+                    plurals[code][source].append(plural)
                     logger(f"Created plural {plural_formula} for language {code}")
 
+                # CLDR and QT plurals should have just a single of them
+                if source != Plural.SOURCE_GETTEXT and len(plurals[code][source]) > 1:
+                    logger(
+                        f"Removing extra {source} plurals for language {code} ({len(plurals[code][source])})!"
+                    )
+                    for extra_plural in plurals[code][source]:
+                        if extra_plural != plural:
+                            extra_plural.translation_set.update(plural=plural)
+                            extra_plural.delete()
+                    plurals[code][source] = [plural]
+
+        # Sync FORMULA_WITH_ZERO
+        for code, language_plurals in plurals.items():
+            if Plural.SOURCE_CLDR_ZERO in language_plurals:
+                if Plural.SOURCE_CLDR not in language_plurals:
+                    logger(f"Missing CLDR plural for {code}!")
+                    continue
+                zero_plural = language_plurals[Plural.SOURCE_CLDR_ZERO][0]
+                cldr_plural = language_plurals[Plural.SOURCE_CLDR][0]
+                current_formula = FORMULA_WITH_ZERO[cldr_plural.formula]
+                if zero_plural.formula != current_formula:
+                    logger(f"Updating CLDR plural with zero for {code}")
+                    zero_plural.formula = current_formula
+                    zero_plural.number = cldr_plural.number + 1
+                    zero_plural.save(update_fields=["formula", "number"])
+
         self._fixup_plural_types(logger)
 
     def _fixup_plural_types(self, logger) -> None: