diff --git a/app/GraphQL/Mutations/CreatePinnedTestMeasurement.php b/app/GraphQL/Mutations/CreatePinnedTestMeasurement.php
index fbf8efae10..6ee73b3490 100644
--- a/app/GraphQL/Mutations/CreatePinnedTestMeasurement.php
+++ b/app/GraphQL/Mutations/CreatePinnedTestMeasurement.php
@@ -4,6 +4,7 @@
 
 namespace App\GraphQL\Mutations;
 
+use App\Exceptions\GraphQLMutationException;
 use App\Models\PinnedTestMeasurement;
 use App\Models\Project;
 use Illuminate\Support\Facades\Gate;
@@ -18,12 +19,18 @@ final class CreatePinnedTestMeasurement extends AbstractMutation
      *     projectId: int,
      *     name: string,
      * } $args
+     *
+     * @throws GraphQLMutationException
      */
     public function __invoke(null $_, array $args): self
     {
         $project = Project::find((int) $args['projectId']);
         Gate::authorize('createPinnedTestMeasurement', $project);
 
+        if ($project?->pinnedTestMeasurements()->where('name', $args['name'])->exists() === true) {
+            throw new GraphQLMutationException('This test measurement is already pinned.');
+        }
+
         $nextAvailablePosition = $project?->pinnedTestMeasurements()->max('position');
         if ($nextAvailablePosition === null) {
             $nextAvailablePosition = 1;
diff --git a/database/migrations/2026_10_25_134934_measurement_unique_name.php b/database/migrations/2026_10_25_134934_measurement_unique_name.php
new file mode 100644
index 0000000000..65dd309d91
--- /dev/null
+++ b/database/migrations/2026_10_25_134934_measurement_unique_name.php
@@ -0,0 +1,25 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Support\Facades\DB;
+
+return new class extends Migration {
+    public function up(): void
+    {
+        // Keep the first-positioned copy of each duplicate, since that's the one displayed.
+        DB::delete('
+            DELETE FROM measurement a
+            USING measurement b
+            WHERE
+                a.projectid = b.projectid
+                AND a.name = b.name
+                AND (a.position, a.id) > (b.position, b.id)
+        ');
+
+        DB::statement('CREATE UNIQUE INDEX ON measurement (projectid, name)');
+    }
+
+    public function down(): void
+    {
+    }
+};
diff --git a/tests/Feature/GraphQL/Mutations/CreatePinnedTestMeasurementTest.php b/tests/Feature/GraphQL/Mutations/CreatePinnedTestMeasurementTest.php
index e355a66990..d1509218d4 100644
--- a/tests/Feature/GraphQL/Mutations/CreatePinnedTestMeasurementTest.php
+++ b/tests/Feature/GraphQL/Mutations/CreatePinnedTestMeasurementTest.php
@@ -195,4 +195,79 @@ public function testCreatesMultipleMeasurementsInOrder(): void
         self::assertContains($name1, $project->pinnedTestMeasurements()->pluck('name')->toArray());
         self::assertContains($name2, $project->pinnedTestMeasurements()->pluck('name')->toArray());
     }
+
+    public function testFailsWhenDuplicateName(): void
+    {
+        $project = $this->makePublicProject();
+        $user = User::factory()->adminUser()->create();
+
+        $name = Str::uuid()->toString();
+        $project->pinnedTestMeasurements()->create([
+            'name' => $name,
+            'position' => 1,
+        ]);
+
+        $this->actingAs($user)->graphQL('
+            mutation createPinnedTestMeasurement($input: CreatePinnedTestMeasurementInput!) {
+                createPinnedTestMeasurement(input: $input) {
+                    message
+                    pinnedTestMeasurement {
+                        name
+                        position
+                    }
+                }
+            }
+        ', [
+            'input' => [
+                'projectId' => $project->id,
+                'name' => $name,
+            ],
+        ])->assertJsonPath('data.createPinnedTestMeasurement', null)
+            ->assertGraphQLErrorMessage('This test measurement is already pinned.');
+
+        self::assertSame([$name], $project->pinnedTestMeasurements()->pluck('name')->toArray());
+    }
+
+    public function testAllowsSameNameInDifferentProjects(): void
+    {
+        $project1 = $this->makePublicProject();
+        $project2 = $this->makePublicProject();
+        $user = User::factory()->adminUser()->create();
+
+        $name = Str::uuid()->toString();
+        $project1->pinnedTestMeasurements()->create([
+            'name' => $name,
+            'position' => 1,
+        ]);
+
+        $this->actingAs($user)->graphQL('
+            mutation createPinnedTestMeasurement($input: CreatePinnedTestMeasurementInput!) {
+                createPinnedTestMeasurement(input: $input) {
+                    message
+                    pinnedTestMeasurement {
+                        name
+                        position
+                    }
+                }
+            }
+        ', [
+            'input' => [
+                'projectId' => $project2->id,
+                'name' => $name,
+            ],
+        ])->assertExactJson([
+            'data' => [
+                'createPinnedTestMeasurement' => [
+                    'message' => null,
+                    'pinnedTestMeasurement' => [
+                        'name' => $name,
+                        'position' => 1,
+                    ],
+                ],
+            ],
+        ]);
+
+        self::assertSame([$name], $project1->pinnedTestMeasurements()->pluck('name')->toArray());
+        self::assertSame([$name], $project2->pinnedTestMeasurements()->pluck('name')->toArray());
+    }
 }