diff --git a/manifest/manifestlist/manifestlist.go b/manifest/manifestlist/manifestlist.go
index 55c0224e..9cc2fc15 100644
--- a/manifest/manifestlist/manifestlist.go
+++ b/manifest/manifestlist/manifestlist.go
@@ -54,6 +54,9 @@ func init() {
 	}
 
 	imageIndexFunc := func(b []byte) (distribution.Manifest, distribution.Descriptor, error) {
+		if err := validateIndex(b); err != nil {
+			return nil, distribution.Descriptor{}, err
+		}
 		m := new(DeserializedManifestList)
 		err := m.UnmarshalJSON(b)
 		if err != nil {
@@ -221,3 +224,23 @@ func (m DeserializedManifestList) Payload() (string, []byte, error) {
 
 	return mediaType, m.canonical, nil
 }
+
+// unknownDocument represents a manifest, manifest list, or index that has not
+// yet been validated
+type unknownDocument struct {
+	Config interface{} `json:"config,omitempty"`
+	Layers interface{} `json:"layers,omitempty"`
+}
+
+// validateIndex returns an error if the byte slice is invalid JSON or if it
+// contains fields that belong to a manifest
+func validateIndex(b []byte) error {
+	var doc unknownDocument
+	if err := json.Unmarshal(b, &doc); err != nil {
+		return err
+	}
+	if doc.Config != nil || doc.Layers != nil {
+		return errors.New("index: expected index but found manifest")
+	}
+	return nil
+}
diff --git a/manifest/manifestlist/manifestlist_test.go b/manifest/manifestlist/manifestlist_test.go
index 860dca51..efbb72e8 100644
--- a/manifest/manifestlist/manifestlist_test.go
+++ b/manifest/manifestlist/manifestlist_test.go
@@ -7,6 +7,8 @@ import (
 	"testing"
 
 	"github.com/distribution/distribution/v3"
+	"github.com/distribution/distribution/v3/manifest/ocischema"
+
 	v1 "github.com/opencontainers/image-spec/specs-go/v1"
 )
 
@@ -327,3 +329,33 @@ func TestMediaTypes(t *testing.T) {
 	mediaTypeTest(t, v1.MediaTypeImageIndex, v1.MediaTypeImageIndex, false)
 	mediaTypeTest(t, v1.MediaTypeImageIndex, v1.MediaTypeImageIndex+"XXX", true)
 }
+
+func TestValidateManifest(t *testing.T) {
+	manifest := ocischema.Manifest{
+		Config: distribution.Descriptor{Size: 1},
+		Layers: []distribution.Descriptor{{Size: 2}},
+	}
+	index := ManifestList{
+		Manifests: []ManifestDescriptor{
+			{Descriptor: distribution.Descriptor{Size: 3}},
+		},
+	}
+	t.Run("valid", func(t *testing.T) {
+		b, err := json.Marshal(index)
+		if err != nil {
+			t.Fatal("unexpected error marshaling index", err)
+		}
+		if err := validateIndex(b); err != nil {
+			t.Error("index should be valid", err)
+		}
+	})
+	t.Run("invalid", func(t *testing.T) {
+		b, err := json.Marshal(manifest)
+		if err != nil {
+			t.Fatal("unexpected error marshaling manifest", err)
+		}
+		if err := validateIndex(b); err == nil {
+			t.Error("manifest should not be valid")
+		}
+	})
+}
diff --git a/manifest/ocischema/manifest.go b/manifest/ocischema/manifest.go
index 968de6e3..e76e4907 100644
--- a/manifest/ocischema/manifest.go
+++ b/manifest/ocischema/manifest.go
@@ -22,6 +22,9 @@ var (
 
 func init() {
 	ocischemaFunc := func(b []byte) (distribution.Manifest, distribution.Descriptor, error) {
+		if err := validateManifest(b); err != nil {
+			return nil, distribution.Descriptor{}, err
+		}
 		m := new(DeserializedManifest)
 		err := m.UnmarshalJSON(b)
 		if err != nil {
@@ -122,3 +125,22 @@ func (m *DeserializedManifest) MarshalJSON() ([]byte, error) {
 func (m DeserializedManifest) Payload() (string, []byte, error) {
 	return v1.MediaTypeImageManifest, m.canonical, nil
 }
+
+// unknownDocument represents a manifest, manifest list, or index that has not
+// yet been validated
+type unknownDocument struct {
+	Manifests interface{} `json:"manifests,omitempty"`
+}
+
+// validateManifest returns an error if the byte slice is invalid JSON or if it
+// contains fields that belong to a index
+func validateManifest(b []byte) error {
+	var doc unknownDocument
+	if err := json.Unmarshal(b, &doc); err != nil {
+		return err
+	}
+	if doc.Manifests != nil {
+		return errors.New("ocimanifest: expected manifest but found index")
+	}
+	return nil
+}
diff --git a/manifest/ocischema/manifest_test.go b/manifest/ocischema/manifest_test.go
index 87a6479e..03b9edcb 100644
--- a/manifest/ocischema/manifest_test.go
+++ b/manifest/ocischema/manifest_test.go
@@ -8,6 +8,8 @@ import (
 
 	"github.com/distribution/distribution/v3"
 	"github.com/distribution/distribution/v3/manifest"
+	"github.com/distribution/distribution/v3/manifest/manifestlist"
+
 	v1 "github.com/opencontainers/image-spec/specs-go/v1"
 )
 
@@ -182,3 +184,33 @@ func TestMediaTypes(t *testing.T) {
 	mediaTypeTest(t, v1.MediaTypeImageManifest, false)
 	mediaTypeTest(t, v1.MediaTypeImageManifest+"XXX", true)
 }
+
+func TestValidateManifest(t *testing.T) {
+	manifest := Manifest{
+		Config: distribution.Descriptor{Size: 1},
+		Layers: []distribution.Descriptor{{Size: 2}},
+	}
+	index := manifestlist.ManifestList{
+		Manifests: []manifestlist.ManifestDescriptor{
+			{Descriptor: distribution.Descriptor{Size: 3}},
+		},
+	}
+	t.Run("valid", func(t *testing.T) {
+		b, err := json.Marshal(manifest)
+		if err != nil {
+			t.Fatal("unexpected error marshaling manifest", err)
+		}
+		if err := validateManifest(b); err != nil {
+			t.Error("manifest should be valid", err)
+		}
+	})
+	t.Run("invalid", func(t *testing.T) {
+		b, err := json.Marshal(index)
+		if err != nil {
+			t.Fatal("unexpected error marshaling index", err)
+		}
+		if err := validateManifest(b); err == nil {
+			t.Error("index should not be valid")
+		}
+	})
+}