diff --git a/internal/imgcache/negative_cache_internal_test.go b/internal/imgcache/negative_cache_internal_test.go
index ded267c..3f7c9c2 100644
--- a/internal/imgcache/negative_cache_internal_test.go
+++ b/internal/imgcache/negative_cache_internal_test.go
@@ -3,6 +3,7 @@ package imgcache
 import (
 	"context"
 	"errors"
+	"strconv"
 	"testing"
 	"time"
 )
@@ -185,6 +186,120 @@ func negativeCacheRowCount(tb testing.TB, cache *Cache, sourcePath string) int {
 	return count
 }
 
+// TestCleanExpiredDeletesInBatches stores one expired negative cache row
+// more than one batch holds, and one row that has not expired. One
+// statement must delete one batch and no more, so a request waits behind
+// one batch at most; CleanExpired must then remove the expired row left
+// over and keep the row that has not expired.
+func TestCleanExpiredDeletesInBatches(t *testing.T) {
+	t.Parallel()
+
+	cache, err := NewCache(evictionTestDB(t), CacheConfig{StateDir: t.TempDir()})
+	if err != nil {
+		t.Fatalf("failed to create cache: %v", err)
+	}
+
+	ctx := t.Context()
+
+	insertExpiredNegativeCacheRows(t, cache, cleanExpiredBatchSize+1)
+
+	const notExpiredPath = "/later.jpg"
+
+	_, err = cache.db.ExecContext(ctx, `
+		INSERT INTO negative_cache
+			(source_host, source_path, status_code, expires_at)
+		VALUES (?, ?, 404, datetime('now', '+1 hour'))
+	`, testHostExample, notExpiredPath)
+	if err != nil {
+		t.Fatalf("failed to insert a row that has not expired: %v", err)
+	}
+
+	deleted, err := cache.cleanExpiredBatch(ctx)
+	if err != nil {
+		t.Fatalf("cleanExpiredBatch failed: %v", err)
+	}
+
+	t.Logf("one statement deleted %d of %d expired rows",
+		deleted, cleanExpiredBatchSize+1)
+
+	if deleted != cleanExpiredBatchSize {
+		t.Errorf("one statement deleted %d rows, want %d",
+			deleted, cleanExpiredBatchSize)
+	}
+
+	err = cache.CleanExpired(ctx)
+	if err != nil {
+		t.Fatalf("CleanExpired failed: %v", err)
+	}
+
+	if count := negativeCacheTableRowCount(t, cache); count != 1 {
+		t.Errorf("negative_cache holds %d rows after CleanExpired, want 1", count)
+	}
+
+	if negativeCacheRowCount(t, cache, notExpiredPath) != 1 {
+		t.Error("the row that has not expired was removed")
+	}
+}
+
+// TestCleanExpiredStopsOnceContextEnds runs CleanExpired with a context
+// that has already ended: it must return the context's error and delete
+// no row.
+func TestCleanExpiredStopsOnceContextEnds(t *testing.T) {
+	t.Parallel()
+
+	cache, err := NewCache(evictionTestDB(t), CacheConfig{StateDir: t.TempDir()})
+	if err != nil {
+		t.Fatalf("failed to create cache: %v", err)
+	}
+
+	insertExpiredNegativeCacheRows(t, cache, 1)
+
+	ctx, cancel := context.WithCancel(t.Context())
+	cancel()
+
+	err = cache.CleanExpired(ctx)
+	if !errors.Is(err, context.Canceled) {
+		t.Errorf("CleanExpired() error = %v, want context.Canceled", err)
+	}
+
+	if count := negativeCacheTableRowCount(t, cache); count != 1 {
+		t.Errorf("negative_cache holds %d rows, want the expired row kept", count)
+	}
+}
+
+// insertExpiredNegativeCacheRows inserts count negative_cache rows that
+// expired an hour ago, each for a different source path.
+func insertExpiredNegativeCacheRows(t *testing.T, cache *Cache, count int) {
+	t.Helper()
+
+	for i := range count {
+		_, err := cache.db.ExecContext(t.Context(), `
+			INSERT INTO negative_cache
+				(source_host, source_path, status_code, expires_at)
+			VALUES (?, ?, 404, datetime('now', '-1 hour'))
+		`, testHostExample, "/expired/"+strconv.Itoa(i)+".jpg")
+		if err != nil {
+			t.Fatalf("failed to insert an expired row: %v", err)
+		}
+	}
+}
+
+// negativeCacheTableRowCount returns how many rows negative_cache holds.
+func negativeCacheTableRowCount(tb testing.TB, cache *Cache) int {
+	tb.Helper()
+
+	var count int
+
+	err := cache.db.QueryRowContext(tb.Context(),
+		`SELECT COUNT(*) FROM negative_cache`,
+	).Scan(&count)
+	if err != nil {
+		tb.Fatalf("failed to count negative_cache rows: %v", err)
+	}
+
+	return count
+}
+
 func TestService_Get_ReturnsErrorForNegativeCachedURL(t *testing.T) {
 	t.Parallel()