diff --git a/app/Services/PrometheusMetricsSummary.php b/app/Services/PrometheusMetricsSummary.php
index 1bd36d124..f96802831 100644
--- a/app/Services/PrometheusMetricsSummary.php
+++ b/app/Services/PrometheusMetricsSummary.php
@@ -400,9 +400,12 @@ private function workerRows(string $namespace, CarbonInterface $now, array $queu
 
     private function selectLatencyBuckets($query, string $durationExpr, string $durationAvailableSql): void
     {
+        // SQLite duration expressions have no affinity, while PDO binds floats as text.
+        $bound = $query->getConnection()->getDriverName() === 'sqlite' ? 'CAST(? AS REAL)' : '?';
+
         foreach (self::LATENCY_BUCKETS_SECONDS as $index => $bucket) {
             $query->selectRaw(
-                "SUM(CASE WHEN {$durationAvailableSql} AND {$durationExpr} <= ? THEN 1 ELSE 0 END) as bucket_{$index}",
+                "SUM(CASE WHEN {$durationAvailableSql} AND {$durationExpr} <= {$bound} THEN 1 ELSE 0 END) as bucket_{$index}",
                 [$bucket],
             );
         }
diff --git a/tests/Feature/SystemPrometheusMetricsTest.php b/tests/Feature/SystemPrometheusMetricsTest.php
index 626b17f8c..239be98e6 100644
--- a/tests/Feature/SystemPrometheusMetricsTest.php
+++ b/tests/Feature/SystemPrometheusMetricsTest.php
@@ -33,6 +33,43 @@ protected function tearDown(): void
         parent::tearDown();
     }
 
+    public function test_latency_buckets_exclude_durations_above_the_bound(): void
+    {
+        $run = $this->workflowRun(
+            workflowId: 'histogram-run',
+            workflowType: 'HistogramWorkflow',
+            queue: 'histogram',
+            status: 'completed',
+            statusBucket: 'completed',
+            durationMs: 2000,
+        );
+        $this->activity($run, 'HistogramActivity', 'histogram', 'completed', 1500);
+
+        $response = $this->getJson(
+            '/api/system/prometheus-metrics',
+            $this->controlPlaneHeadersWithWorkerProtocol(),
+        );
+
+        $response->assertOk()
+            ->assertJsonPath('series.workflows.0.latency_seconds.count', 1)
+            ->assertJsonPath('series.activities.0.latency_seconds.count', 1);
+
+        $expected = [
+            '0.1' => 0,
+            '0.5' => 0,
+            '1' => 0,
+            '2.5' => 1,
+            '5' => 1,
+            '10' => 1,
+            '30' => 1,
+            '60' => 1,
+            '300' => 1,
+            '900' => 1,
+        ];
+        $this->assertSame($expected, $response->json('series.workflows.0.latency_seconds.buckets'));
+        $this->assertSame($expected, $response->json('series.activities.0.latency_seconds.buckets'));
+    }
+
     public function test_prometheus_metrics_summary_is_granular_by_queue_workflow_and_activity_type(): void
     {
         $runA = $this->workflowRun(
@@ -554,6 +591,8 @@ private function workflowRun(
     private function activity(string $runId, string $activityType, string $queue, string $status, int $durationMs): void
     {
         $startedAt = now()->subSeconds(10);
+        // Query-builder DateTime bindings would discard the fixture's fractional second.
+        $closedAt = $startedAt->copy()->addMilliseconds($durationMs)->format('Y-m-d H:i:s.u');
 
         DB::table('activity_executions')->insert([
             'id' => (string) Str::ulid(),
@@ -564,9 +603,9 @@ private function activity(string $runId, string $activityType, string $queue, st
             'status' => $status,
             'queue' => $queue,
             'started_at' => $startedAt,
-            'closed_at' => $startedAt->copy()->addMilliseconds($durationMs),
+            'closed_at' => $closedAt,
             'created_at' => $startedAt,
-            'updated_at' => $startedAt->copy()->addMilliseconds($durationMs),
+            'updated_at' => $closedAt,
         ]);
     }