diff --git a/tests/unit/oidc/forms/test_gitlab.py b/tests/unit/oidc/forms/test_gitlab.py
index a8a0f1ea5723..707db19c9f23 100644
--- a/tests/unit/oidc/forms/test_gitlab.py
+++ b/tests/unit/oidc/forms/test_gitlab.py
@@ -116,6 +116,45 @@ def test_validate_basic_invalid_fields(self, monkeypatch, data):
         # We're testing only the basic validation here.
         assert not form.validate()
 
+    @pytest.mark.parametrize(
+        "project_name",
+        ["invalid.git", "invalid.atom", "invalid--project"],
+    )
+    def test_reserved_project_names(self, project_name):
+
+        data = MultiDict(
+            {
+                "namespace": "some",
+                "workflow_filepath": "subfolder/some-workflow.yml",
+                "project": project_name,
+            }
+        )
+
+        form = gitlab.GitLabPublisherForm(data)
+        assert not form.validate()
+
+    @pytest.mark.parametrize(
+        "namespace",
+        [
+            "invalid.git",
+            "invalid.atom",
+            "consecutive--special-characters",
+            "must-end-with-non-special-characters-",
+        ],
+    )
+    def test_reserved_organization_names(self, namespace):
+
+        data = MultiDict(
+            {
+                "namespace": namespace,
+                "workflow_filepath": "subfolder/some-workflow.yml",
+                "project": "valid-project",
+            }
+        )
+
+        form = gitlab.GitLabPublisherForm(data)
+        assert not form.validate()
+
     @pytest.mark.parametrize(
         "workflow_filepath",
         [
diff --git a/warehouse/locale/messages.pot b/warehouse/locale/messages.pot
index d58b052f03c7..c2e53f065d36 100644
--- a/warehouse/locale/messages.pot
+++ b/warehouse/locale/messages.pot
@@ -369,7 +369,7 @@ msgid "Select project"
 msgstr ""
 
 #: warehouse/manage/forms.py:495 warehouse/oidc/forms/_core.py:23
-#: warehouse/oidc/forms/gitlab.py:44
+#: warehouse/oidc/forms/gitlab.py:58
 msgid "Specify project name"
 msgstr ""
 
@@ -574,7 +574,8 @@ msgstr ""
 msgid "Expired invitation for '${username}' deleted."
 msgstr ""
 
-#: warehouse/oidc/forms/_core.py:25 warehouse/oidc/forms/gitlab.py:46
+#: warehouse/oidc/forms/_core.py:25 warehouse/oidc/forms/gitlab.py:61
+#: warehouse/oidc/forms/gitlab.py:65
 msgid "Invalid project name"
 msgstr ""
 
@@ -678,26 +679,30 @@ msgid "Workflow filename must be a filename only, without directories"
 msgstr ""
 
 #: warehouse/oidc/forms/gitlab.py:33
+msgid "Name ends with .git or .atom"
+msgstr ""
+
+#: warehouse/oidc/forms/gitlab.py:42
 msgid "Specify GitLab namespace (username or group/subgroup)"
 msgstr ""
 
-#: warehouse/oidc/forms/gitlab.py:37
+#: warehouse/oidc/forms/gitlab.py:47 warehouse/oidc/forms/gitlab.py:51
 msgid "Invalid GitLab username or group/subgroup name."
 msgstr ""
 
-#: warehouse/oidc/forms/gitlab.py:54
+#: warehouse/oidc/forms/gitlab.py:73
 msgid "Specify top-level pipeline file path"
 msgstr ""
 
-#: warehouse/oidc/forms/gitlab.py:63
+#: warehouse/oidc/forms/gitlab.py:82
 msgid "Invalid environment name"
 msgstr ""
 
-#: warehouse/oidc/forms/gitlab.py:78
+#: warehouse/oidc/forms/gitlab.py:97
 msgid "Top-level pipeline file path must end with .yml or .yaml"
 msgstr ""
 
-#: warehouse/oidc/forms/gitlab.py:82
+#: warehouse/oidc/forms/gitlab.py:101
 msgid "Top-level pipeline file path cannot start or end with /"
 msgstr ""
 
diff --git a/warehouse/oidc/forms/gitlab.py b/warehouse/oidc/forms/gitlab.py
index a861dadd2d01..eb940d781a81 100644
--- a/warehouse/oidc/forms/gitlab.py
+++ b/warehouse/oidc/forms/gitlab.py
@@ -11,6 +11,7 @@
 # limitations under the License.
 
 import re
+import typing
 
 import wtforms
 
@@ -19,10 +20,18 @@
 from warehouse.oidc.forms._core import PendingPublisherMixin
 
 # https://docs.gitlab.com/ee/user/reserved_names.html#limitations-on-project-and-group-names
-_VALID_GITLAB_PROJECT = re.compile(r"^[a-zA-Z0-9][a-zA-Z0-9-_.]*$")
-_VALID_GITLAB_NAMESPACE = re.compile(r"^[a-zA-Z0-9][a-zA-Z0-9-_./]*$")
+_VALID_GITLAB_PROJECT = re.compile(r"^[a-zA-Z0-9][a-zA-Z0-9_.-]*[a-zA-Z0-9]$")
+_VALID_GITLAB_NAMESPACE = re.compile(r"^[a-zA-Z0-9][a-zA-Z0-9-_./+]*[a-zA-Z0-9]$")
 _VALID_GITLAB_ENVIRONMENT = re.compile(r"^[a-zA-Z0-9\-_/${} ]+$")
 
+_CONSECUTIVE_SPECIAL_CHARACTERS = re.compile(r"(?!.*[._-]{2})")
+
+
+def ends_with_atom_or_git(form: forms.Form, field: wtforms.Field) -> None:
+    field_value = typing.cast(str, field.data).lower()
+    if field_value.endswith(".atom") or field_value.endswith(".git"):
+        raise wtforms.validators.ValidationError(_("Name ends with .git or .atom"))
+
 
 class GitLabPublisherBase(forms.Form):
     __params__ = ["namespace", "project", "workflow_filepath", "environment"]
@@ -32,19 +41,29 @@ class GitLabPublisherBase(forms.Form):
             wtforms.validators.InputRequired(
                 message=_("Specify GitLab namespace (username or group/subgroup)"),
             ),
+            ends_with_atom_or_git,
             wtforms.validators.Regexp(
                 _VALID_GITLAB_NAMESPACE,
                 message=_("Invalid GitLab username or group/subgroup name."),
             ),
+            wtforms.validators.Regexp(
+                _CONSECUTIVE_SPECIAL_CHARACTERS,
+                message=_("Invalid GitLab username or group/subgroup name."),
+            ),
         ]
     )
 
     project = wtforms.StringField(
         validators=[
             wtforms.validators.InputRequired(message=_("Specify project name")),
+            ends_with_atom_or_git,
             wtforms.validators.Regexp(
                 _VALID_GITLAB_PROJECT, message=_("Invalid project name")
             ),
+            wtforms.validators.Regexp(
+                _CONSECUTIVE_SPECIAL_CHARACTERS,
+                message=_("Invalid project name"),
+            ),
         ]
     )