diff --git a/internal/cache/cache.go b/internal/cache/cache.go
index 8be4597..1caf7d1 100644
--- a/internal/cache/cache.go
+++ b/internal/cache/cache.go
@@ -51,7 +51,10 @@ func Open(path, lockPath string) (*Store, error) {
 		}
 	}
 
-	return &Store{db: db, lock: flock.New(lockPath)}, nil
+	store := &Store{db: db, lock: flock.New(lockPath)}
+	// Prune expired entries on startup to prevent unbounded growth.
+	_ = store.Prune()
+	return store, nil
 }
 
 func (s *Store) Close() error {
@@ -61,6 +64,20 @@ func (s *Store) Close() error {
 	return s.db.Close()
 }
 
+// Prune deletes all cache entries whose TTL has fully expired (age > ttl).
+// It is called automatically on Open and can be called manually.
+func (s *Store) Prune() error {
+	if s == nil || s.db == nil {
+		return nil
+	}
+	nowUnix := time.Now().UTC().Unix()
+	_, err := s.db.Exec("DELETE FROM cache_entries WHERE created_at + ttl_seconds < ?", nowUnix)
+	if err != nil {
+		return fmt.Errorf("prune cache: %w", err)
+	}
+	return nil
+}
+
 func (s *Store) Get(key string, maxStale time.Duration) (Result, error) {
 	var value []byte
 	var createdUnix int64
diff --git a/internal/cache/cache_test.go b/internal/cache/cache_test.go
index 3b537a7..a36abe1 100644
--- a/internal/cache/cache_test.go
+++ b/internal/cache/cache_test.go
@@ -56,3 +56,46 @@ func TestCacheTooStale(t *testing.T) {
 		t.Fatalf("expected too stale, got %+v", res)
 	}
 }
+
+func TestPruneRemovesExpiredEntries(t *testing.T) {
+	tmp := t.TempDir()
+	store, err := Open(filepath.Join(tmp, "cache.db"), filepath.Join(tmp, "cache.lock"))
+	if err != nil {
+		t.Fatalf("Open cache failed: %v", err)
+	}
+	defer store.Close()
+
+	// Insert an entry with a very short TTL.
+	if err := store.Set("prunable", []byte(`"old"`), 1*time.Second); err != nil {
+		t.Fatalf("Set failed: %v", err)
+	}
+	// Insert a long-lived entry.
+	if err := store.Set("keeper", []byte(`"keep"`), 1*time.Hour); err != nil {
+		t.Fatalf("Set failed: %v", err)
+	}
+
+	// Wait for the short entry to expire.
+	time.Sleep(1200 * time.Millisecond)
+
+	if err := store.Prune(); err != nil {
+		t.Fatalf("Prune failed: %v", err)
+	}
+
+	// The expired entry should be gone (miss).
+	res, err := store.Get("prunable", 1*time.Hour)
+	if err != nil {
+		t.Fatalf("Get prunable failed: %v", err)
+	}
+	if res.Hit {
+		t.Fatalf("expected prunable to be evicted, but got hit")
+	}
+
+	// The long-lived entry should still be there.
+	res, err = store.Get("keeper", 1*time.Hour)
+	if err != nil {
+		t.Fatalf("Get keeper failed: %v", err)
+	}
+	if !res.Hit {
+		t.Fatalf("expected keeper to still be present")
+	}
+}