diff --git a/tests/unit/oidc/forms/test_activestate.py b/tests/unit/oidc/forms/test_activestate.py
index f9b0d8574d2c..e6a38094e081 100644
--- a/tests/unit/oidc/forms/test_activestate.py
+++ b/tests/unit/oidc/forms/test_activestate.py
@@ -68,7 +68,7 @@ def test_validate_project_name_already_in_use_owner(self, pyramid_config):
         owners = [user]
 
         def check_project_name(name):
-            return ProjectNameUnavailableExistingError(
+            raise ProjectNameUnavailableExistingError(
                 existing_project=pretend.stub(owners=owners)
             )
 
@@ -98,7 +98,7 @@ def test_validate_project_name_already_in_use_not_owner(self, pyramid_config):
         owners = []
 
         def check_project_name(name):
-            return ProjectNameUnavailableExistingError(
+            raise ProjectNameUnavailableExistingError(
                 existing_project=pretend.stub(owners=owners)
             )
 
diff --git a/tests/unit/oidc/forms/test_github.py b/tests/unit/oidc/forms/test_github.py
index f7930528b338..c1b1f2ec193d 100644
--- a/tests/unit/oidc/forms/test_github.py
+++ b/tests/unit/oidc/forms/test_github.py
@@ -65,12 +65,15 @@ def test_validate_project_name_already_in_use_owner(self, pyramid_config):
         user = pretend.stub()
         owners = [user]
 
+        def check_project_name(name):
+            raise ProjectNameUnavailableExistingError(
+                existing_project=pretend.stub(owners=owners)
+            )
+
         form = github.PendingGitHubPublisherForm(
             api_token="fake-token",
             route_url=route_url,
-            check_project_name=lambda name: ProjectNameUnavailableExistingError(
-                existing_project=pretend.stub(owners=owners)
-            ),
+            check_project_name=check_project_name,
             user=user,
         )
 
@@ -93,12 +96,15 @@ def test_validate_project_name_already_in_use_not_owner(self, pyramid_config):
         user = pretend.stub()
         owners = []
 
+        def check_project_name(name):
+            raise ProjectNameUnavailableExistingError(
+                existing_project=pretend.stub(owners=owners)
+            )
+
         form = github.PendingGitHubPublisherForm(
             api_token="fake-token",
             route_url=route_url,
-            check_project_name=lambda name: ProjectNameUnavailableExistingError(
-                existing_project=pretend.stub(owners=owners)
-            ),
+            check_project_name=check_project_name,
             user=user,
         )
 
@@ -119,10 +125,13 @@ def test_validate_project_name_already_in_use_not_owner(self, pyramid_config):
         ],
     )
     def test_validate_project_name_unavailable(self, reason, pyramid_config):
+        def check_project_name(name):
+            raise reason
+
         form = github.PendingGitHubPublisherForm(
             api_token="fake-token",
             route_url=pretend.call_recorder(lambda *args, **kwargs: ""),
-            check_project_name=lambda name: reason,
+            check_project_name=check_project_name,
             user=pretend.stub(),
         )
 
diff --git a/tests/unit/oidc/forms/test_gitlab.py b/tests/unit/oidc/forms/test_gitlab.py
index cd50060e81f7..dd6c2d887106 100644
--- a/tests/unit/oidc/forms/test_gitlab.py
+++ b/tests/unit/oidc/forms/test_gitlab.py
@@ -54,11 +54,14 @@ def test_validate_project_name_already_in_use_owner(self, pyramid_config):
         owners = [user]
         route_url = pretend.call_recorder(lambda *args, **kwargs: "my_url")
 
+        def check_project_name(name):
+            raise ProjectNameUnavailableExistingError(
+                existing_project=pretend.stub(owners=owners)
+            )
+
         form = gitlab.PendingGitLabPublisherForm(
             route_url=route_url,
-            check_project_name=lambda name: ProjectNameUnavailableExistingError(
-                existing_project=pretend.stub(owners=owners)
-            ),
+            check_project_name=check_project_name,
             user=user,
         )
 
@@ -81,11 +84,14 @@ def test_validate_project_name_already_in_use_not_owner(self, pyramid_config):
         owners = []
         route_url = pretend.call_recorder(lambda *args, **kwargs: "my_url")
 
+        def check_project_name(name):
+            raise ProjectNameUnavailableExistingError(
+                existing_project=pretend.stub(owners=owners)
+            )
+
         form = gitlab.PendingGitLabPublisherForm(
             route_url=route_url,
-            check_project_name=lambda name: ProjectNameUnavailableExistingError(
-                existing_project=pretend.stub(owners=owners)
-            ),
+            check_project_name=check_project_name,
             user=user,
         )
 
diff --git a/tests/unit/oidc/forms/test_google.py b/tests/unit/oidc/forms/test_google.py
index 9cb014a24801..cca87c6637c5 100644
--- a/tests/unit/oidc/forms/test_google.py
+++ b/tests/unit/oidc/forms/test_google.py
@@ -51,11 +51,15 @@ def test_validate_project_name_already_in_use_owner(self, pyramid_config):
         user = pretend.stub()
         owners = [user]
         route_url = pretend.call_recorder(lambda *args, **kwargs: "my_url")
+
+        def check_project_name(name):
+            raise ProjectNameUnavailableExistingError(
+                existing_project=pretend.stub(owners=owners)
+            )
+
         form = google.PendingGooglePublisherForm(
             route_url=route_url,
-            check_project_name=lambda name: ProjectNameUnavailableExistingError(
-                existing_project=pretend.stub(owners=owners)
-            ),
+            check_project_name=check_project_name,
             user=user,
         )
 
@@ -77,11 +81,15 @@ def test_validate_project_name_already_in_use_not_owner(self, pyramid_config):
         user = pretend.stub()
         owners = []
         route_url = pretend.call_recorder(lambda *args, **kwargs: "my_url")
+
+        def check_project_name(name):
+            raise ProjectNameUnavailableExistingError(
+                existing_project=pretend.stub(owners=owners)
+            )
+
         form = google.PendingGooglePublisherForm(
             route_url=route_url,
-            check_project_name=lambda name: ProjectNameUnavailableExistingError(
-                existing_project=pretend.stub(owners=owners)
-            ),
+            check_project_name=check_project_name,
             user=user,
         )
 
diff --git a/warehouse/oidc/forms/_core.py b/warehouse/oidc/forms/_core.py
index 75765a272a79..8ce51bcc0e80 100644
--- a/warehouse/oidc/forms/_core.py
+++ b/warehouse/oidc/forms/_core.py
@@ -36,55 +36,54 @@ class PendingPublisherMixin:
     def validate_project_name(self, field):
         project_name = field.data
 
-        match self._check_project_name(project_name):
-            case ProjectNameUnavailableInvalidError():
-                raise wtforms.validators.ValidationError(_("Invalid project name"))
-            case ProjectNameUnavailableExistingError(existing_project=existing_project):
-                # If the user owns the existing project, the error message includes a
-                # link to the project settings that the user can modify.
-                if self._user in existing_project.owners:
-                    url_params = {
-                        name: value for name, value in self.data.items() if value
-                    }
-                    url_params["provider"] = {self.provider}
-                    url = self._route_url(
-                        "manage.project.settings.publishing",
-                        project_name=project_name,
-                        _query=url_params,
-                    )
+        try:
+            self._check_project_name(project_name)
+        except ProjectNameUnavailableInvalidError:
+            raise wtforms.validators.ValidationError(_("Invalid project name"))
+        except ProjectNameUnavailableExistingError as e:
+            # If the user owns the existing project, the error message includes a
+            # link to the project settings that the user can modify.
+            if self._user in e.existing_project.owners:
+                url_params = {name: value for name, value in self.data.items() if value}
+                url_params["provider"] = {self.provider}
+                url = self._route_url(
+                    "manage.project.settings.publishing",
+                    project_name=project_name,
+                    _query=url_params,
+                )
 
-                    # We mark the error message as safe, so that the HTML hyperlink is
-                    # not escaped by Jinja
-                    raise wtforms.validators.ValidationError(
-                        markupsafe.Markup(
-                            _(
-                                "This project already exists: use the project's "
-                                "publishing settings <a href='${url}'>here</a> to "
-                                "create a Trusted Publisher for it.",
-                                mapping={"url": url},
-                            )
+                # We mark the error message as safe, so that the HTML hyperlink is
+                # not escaped by Jinja
+                raise wtforms.validators.ValidationError(
+                    markupsafe.Markup(
+                        _(
+                            "This project already exists: use the project's "
+                            "publishing settings <a href='${url}'>here</a> to "
+                            "create a Trusted Publisher for it.",
+                            mapping={"url": url},
                         )
                     )
-                else:
-                    raise wtforms.validators.ValidationError(
-                        _("This project already exists.")
-                    )
-
-            case ProjectNameUnavailableProhibitedError():
-                raise wtforms.validators.ValidationError(
-                    _("This project name isn't allowed")
                 )
-            case ProjectNameUnavailableSimilarError():
+            else:
                 raise wtforms.validators.ValidationError(
-                    _("This project name is too similar to an existing project")
+                    _("This project already exists.")
                 )
-            case ProjectNameUnavailableStdlibError():
-                raise wtforms.validators.ValidationError(
-                    _(
-                        "This project name isn't allowed (conflict with the Python"
-                        " standard library module name)"
-                    )
+
+        except ProjectNameUnavailableProhibitedError:
+            raise wtforms.validators.ValidationError(
+                _("This project name isn't allowed")
+            )
+        except ProjectNameUnavailableSimilarError:
+            raise wtforms.validators.ValidationError(
+                _("This project name is too similar to an existing project")
+            )
+        except ProjectNameUnavailableStdlibError:
+            raise wtforms.validators.ValidationError(
+                _(
+                    "This project name isn't allowed (conflict with the Python"
+                    " standard library module name)"
                 )
+            )
 
     @property
     def provider(self) -> str:  # pragma: no cover