diff --git a/tests/integration/dry_run_test.go b/tests/integration/dry_run_test.go
index 177e1244f..9e207e18f 100644
--- a/tests/integration/dry_run_test.go
+++ b/tests/integration/dry_run_test.go
@@ -1,11 +1,17 @@
 package integration_test
 
 import (
+	"os"
 	"path/filepath"
+	"strings"
 
 	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
 )
 
+// dockerTransportPrefix is the "docker://" transport prefix used in mapping.txt entries.
+const dockerTransportPrefix = "docker://"
+
 var _ = Describe("dry-run", func() {
 	var workDir string
 	BeforeEach(func() {
@@ -65,4 +71,57 @@ var _ = Describe("dry-run", func() {
 			expectNoRepositoriesInRegistry(*testRegistry)
 		})
 	})
+
+	Describe("mirrorToDisk dry-run with a manifest list image", func() {
+		iscManifestList := filepath.Join("dry_run", "isc-manifest-list.yaml")
+		topLevelSource := "docker://quay.io/openshifttest/hello-openshift@sha256:61b8f5e1a3b5dbd9e2c35fd448dc5106337d7a299873dd3a6f0cd8d4891ecc27"
+
+		// The digest above resolves to a manifest list (image index) with these two
+		// platform-specific sub-manifests, which never change since it's pinned by digest.
+		manifestListSubDigests := []string{
+			"sha256:685a0ca5f33d9f921966c9d9f5922e266affbf93dde0c156709ecdea362f88f4",
+			"sha256:a51d6da571b2e1f57249f4d966af65cbfb361dad66cde7121c1bb656ab196269",
+		}
+
+		It("should include manifest list sub-digests in mapping.txt (OCPBUGS-66263)", func() {
+			By("running mirrorToDisk with --dry-run-manifest-lists")
+			result, err := runner.MirrorToDisk(ctx, filepath.Join(iscDir, iscManifestList), workDir,
+				"--remove-signatures=true", "--dry-run-manifest-lists")
+			expectOcMirrorCommandSuccess(result, err)
+
+			By("verifying mapping.txt contains an entry for each manifest list sub-digest")
+			expectMappingContainsManifestListSubDigests(workDir, topLevelSource, manifestListSubDigests)
+		})
+	})
 })
+
+// expectMappingContainsManifestListSubDigests verifies that mapping.txt contains one extra
+// line per manifest list sub-digest, each re-pinned to the top-level destination's repository.
+// Guards against OCPBUGS-66263, where sub-manifest digests were dropped from the mapping file.
+func expectMappingContainsManifestListSubDigests(workDir, topLevelSource string, subDigests []string) {
+	mappingPath := filepath.Join(workDir, dirWorkingDir, "dry-run", "mapping.txt")
+	data, err := os.ReadFile(mappingPath)
+	Expect(err).NotTo(HaveOccurred(), "mapping.txt not found at: %s", mappingPath)
+
+	mappings := make(map[string]string)
+	for _, line := range strings.Split(strings.TrimSpace(string(data)), "\n") {
+		parts := strings.SplitN(line, "=", 2)
+		Expect(parts).To(HaveLen(2), "mapping line does not follow source=destination format: %s", line)
+		mappings[parts[0]] = parts[1]
+	}
+
+	destination, found := mappings[topLevelSource]
+	Expect(found).To(BeTrue(), "mapping.txt does not contain top-level entry for %q", topLevelSource)
+
+	sourceBase, _, _ := strings.Cut(topLevelSource, "@")
+	// referenceWithoutTagOrDigest expects a bare image reference, so the "docker://" transport
+	// prefix (present on mapping.txt destinations) must be stripped before parsing and restored
+	// afterwards to rebuild a destination in the same format written by oc-mirror.
+	destBase := dockerTransportPrefix + referenceWithoutTagOrDigest(strings.TrimPrefix(destination, dockerTransportPrefix))
+	for _, digest := range subDigests {
+		subSource := sourceBase + "@" + digest
+		subDest := destBase + "@" + digest
+		Expect(mappings).To(HaveKeyWithValue(subSource, subDest),
+			"mapping.txt is missing sub-digest entry %q -> %q", subSource, subDest)
+	}
+}
diff --git a/tests/integration/testdata/imagesetconfigs/dry_run/isc-manifest-list.yaml b/tests/integration/testdata/imagesetconfigs/dry_run/isc-manifest-list.yaml
new file mode 100644
index 000000000..3e92ed036
--- /dev/null
+++ b/tests/integration/testdata/imagesetconfigs/dry_run/isc-manifest-list.yaml
@@ -0,0 +1,9 @@
+# ImageSetConfig to test dry-run mapping of a manifest list (multi-arch) additional image.
+# quay.io/openshifttest/hello-openshift@sha256:61b8f5e1a3b5dbd9e2c35fd448dc5106337d7a299873dd3a6f0cd8d4891ecc27
+# is a manifest list with two platform-specific sub-manifests (arm64, ppc64le), used to verify that
+# dry-run mapping.txt includes an entry for each sub-digest (OCPBUGS-66263).
+kind: ImageSetConfiguration
+apiVersion: mirror.openshift.io/v2alpha1
+mirror:
+  additionalImages:
+  - name: quay.io/openshifttest/hello-openshift@sha256:61b8f5e1a3b5dbd9e2c35fd448dc5106337d7a299873dd3a6f0cd8d4891ecc27