diff --git a/src/app/features/issue/providers/gitlab/gitlab-cfg-form.const.spec.ts b/src/app/features/issue/providers/gitlab/gitlab-cfg-form.const.spec.ts
index 69b22d7d55..2d9a44c55d 100644
--- a/src/app/features/issue/providers/gitlab/gitlab-cfg-form.const.spec.ts
+++ b/src/app/features/issue/providers/gitlab/gitlab-cfg-form.const.spec.ts
@@ -29,9 +29,9 @@ describe('GITLAB_PROJECT_REGEX', () => {
       'a.b-c/d_e',
       'group%2Fproject',
       'group%2Fsub%2Fproject',
-      // GitLab allows consecutive hyphens in a path segment; must not be rejected.
-      'foo--bar',
-      'single',
+      // GitLab allows consecutive hyphens in a path segment; must not be rejected
+      // (as long as the reference is still namespace-qualified).
+      'group/foo--bar',
       '12345',
     ];
     validCases.forEach((value) => {
@@ -42,8 +42,9 @@ describe('GITLAB_PROJECT_REGEX', () => {
   });
 
   describe('invalid project identifiers', () => {
-    // Regression for #8665: a display name with a space must be rejected inline
-    // instead of producing a confusing 404 at poll time.
+    // Regression for #8665: both a display name with a space AND a bare
+    // single-segment slug (which the REST API can never resolve, so it 404s at
+    // poll time) must be rejected inline instead.
     const invalidCases = [
       'My Group/My Gitlab',
       'group/Test Gitlab',
@@ -52,6 +53,10 @@ describe('GITLAB_PROJECT_REGEX', () => {
       'trailingSpace ',
       'https://gitlab.com/foo/bar',
       'foo/bar?scope=all',
+      // Missing namespace — the exact value from the #8665 logs.
+      'test_config',
+      'single',
+      'foo--bar',
     ];
     invalidCases.forEach((value) => {
       it(`rejects "${value}"`, () => {
diff --git a/src/app/features/issue/providers/gitlab/gitlab-cfg-form.const.ts b/src/app/features/issue/providers/gitlab/gitlab-cfg-form.const.ts
index 247047acff..1be44f9758 100644
--- a/src/app/features/issue/providers/gitlab/gitlab-cfg-form.const.ts
+++ b/src/app/features/issue/providers/gitlab/gitlab-cfg-form.const.ts
@@ -8,14 +8,15 @@ import {
   CROSS_ORIGIN_WARNING,
   ISSUE_PROVIDER_COMMON_FORM_FIELDS,
 } from '../../common-issue-form-stuff.const';
-// Matches either a numeric project ID or a path (namespace/project-slug, or its
-// %2F-encoded form). Anchored at both ends: without a leading `^` the original
-// pattern only matched a valid *tail*, so display names with spaces (e.g.
-// "My Group/My Gitlab") passed validation and produced a 404 at poll time (#8665).
-// This is a "did you paste a display name?" sanity guard, not a strict GitLab
-// path validator, so the char class stays permissive (e.g. accepts consecutive
-// hyphens, which GitLab paths allow) rather than risk false-rejecting valid paths.
-export const GITLAB_PROJECT_REGEX = /^(?:[1-9][0-9]*|[\w%./-]+)$/i;
+// A GitLab project reference is EITHER a numeric project ID OR a namespace-qualified
+// path (`group/project`, subgroups, or the `%2F`-encoded form) — the REST API has no
+// way to resolve a project by a bare slug, so a single-segment name like `test_config`
+// always 404s at poll time (#8665). Require a path separator (`/` or `%2F`) for the
+// non-numeric branch so that mistake gets inline feedback instead. Still permissive
+// about the segment chars (e.g. consecutive hyphens, which GitLab paths allow) to
+// avoid false-rejecting valid paths; the separator lookahead keeps the char class a
+// single unnested quantifier (no catastrophic backtracking).
+export const GITLAB_PROJECT_REGEX = /^(?:[1-9][0-9]*|(?=.*(?:\/|%2F))[\w.%/-]+)$/i;
 
 export const GITLAB_CONFIG_FORM: LimitedFormlyFieldConfig<IssueProviderGitlab>[] = [
   ...CROSS_ORIGIN_WARNING,