diff --git a/lib/insights/velocity.ts b/lib/insights/velocity.ts
index 7cf123e..c01c45e 100644
--- a/lib/insights/velocity.ts
+++ b/lib/insights/velocity.ts
@@ -33,7 +33,12 @@ export async function getVelocity(userId: string, sprintsBack = 5): Promise<Velo
   })
 
   // Reverse to chronological order (oldest first, for x-axis)
-  const chronological = [...sprints].filter(s => s.completed_at != null).reverse()
+  // Type-guard so the narrowed array carries `completed_at: Date` (not Date | null).
+  // A `.filter(s => s.completed_at != null)` alone does NOT narrow the element type.
+  type SprintWithCompletedAt = (typeof sprints)[number] & { completed_at: Date }
+  const chronological = [...sprints]
+    .filter((s): s is SprintWithCompletedAt => s.completed_at != null)
+    .reverse()
 
   const result: VelocitySprint[] = chronological.map(sprint => ({
     sprintId: sprint.id,