diff --git a/src/pwa_pages/project_inventory.py b/src/pwa_pages/project_inventory.py
index 5d8cb136..dc4cbcef 100644
--- a/src/pwa_pages/project_inventory.py
+++ b/src/pwa_pages/project_inventory.py
@@ -3,6 +3,7 @@
 import argparse
 import json
 import re
+import sys
 from datetime import datetime
 from functools import partial
 from pathlib import Path
@@ -14,6 +15,11 @@
 
 from .repo import Repo, get_repo
 
+if sys.version_info < (3, 11):
+    from typing_extensions import Self
+else:
+    from typing import Self
+
 
 def load_yaml(path: Union[Path, str]) -> dict:
     with open(path) as stream:
@@ -89,11 +95,11 @@ class ProjectInventory(BaseModel):
     projects: List[Project]
     collaborations: Dict[str, str] = {}
 
-    @model_validator(mode="before")
-    def _check_collaboration_exists(cls, values: dict) -> dict:  # noqa: N805
-        defined_collaborations = set(values["collaborations"])
+    @model_validator(mode="after")
+    def _check_collaboration_exists(self) -> Self:
+        defined_collaborations = set(self.collaborations)
         project: Project
-        for project in values["projects"]:
+        for project in self.projects:
             if project.collaboration is None:
                 continue
             if isinstance(project.collaboration, str):
@@ -104,7 +110,7 @@ def _check_collaboration_exists(cls, values: dict) -> dict:  # noqa: N805
                 if col not in defined_collaborations:
                     msg = f"No collaboration defined for {col}"
                     raise ValueError(msg)
-        return values
+        return self
 
 
 def _create_project_entry(project: Project) -> str: