diff --git a/ipld/car/v2/blockstore/doc.go b/ipld/car/v2/blockstore/doc.go
index c2cf62a80..ddbcc98e6 100644
--- a/ipld/car/v2/blockstore/doc.go
+++ b/ipld/car/v2/blockstore/doc.go
@@ -3,10 +3,9 @@
 //
 // The ReadOnly blockstore provides a read-only random access from a given data payload either in
 // unindexed v1 format or indexed/unindexed v2 format:
-// - ReadOnly.ReadOnlyOf can be used to instantiate a new read-only blockstore for a given CAR v1
-//   data payload and an existing index. See index.Generate for index generation from CAR v1
-//   payload.
-// - ReadOnly.OpenReadOnly can be used to instantiate a new read-only blockstore for a given CAR v2
+// * ReadOnly.NewReadOnly can be used to instantiate a new read-only blockstore for a given CAR v1
+//   or CAR v2 data payload with an optional index override.
+// * ReadOnly.OpenReadOnly can be used to instantiate a new read-only blockstore for a given CAR v2
 //   file with automatic index generation if the index is not present in the given file. This
 //   function can optionally attach the index to the given CAR v2 file.
 //
diff --git a/ipld/car/v2/blockstore/readonly.go b/ipld/car/v2/blockstore/readonly.go
index 521f30280..4125cc1aa 100644
--- a/ipld/car/v2/blockstore/readonly.go
+++ b/ipld/car/v2/blockstore/readonly.go
@@ -42,10 +42,47 @@ type ReadOnly struct {
 	carv2Closer io.Closer
 }
 
-// ReadOnlyOf opens ReadOnly blockstore from an existing backing containing a CAR v1 payload and an existing index.
-// The index for a CAR v1 payload can be separately generated using index.Generate.
-func ReadOnlyOf(backing io.ReaderAt, index index.Index) *ReadOnly {
-	return &ReadOnly{backing: backing, idx: index}
+// NewReadOnly creates a new ReadOnly blockstore from the backing with a optional index as idx.
+// This function accepts both CAR v1 and v2 backing.
+// The blockstore is instantiated with the given index if it is not nil.
+//
+// Otherwise:
+// * For a CAR v1 backing an index is generated.
+// * For a CAR v2 backing an index is only generated if Header.HasIndex returns false.
+//
+// There is no need to call ReadOnly.Close on instances returned by this function.
+func NewReadOnly(backing io.ReaderAt, idx index.Index) (*ReadOnly, error) {
+	version, err := carv2.ReadVersion(internalio.NewOffsetReader(backing, 0))
+	if err != nil {
+		return nil, err
+	}
+	switch version {
+	case 1:
+		if idx == nil {
+			if idx, err = index.Generate(backing); err != nil {
+				return nil, err
+			}
+		}
+		return &ReadOnly{backing: backing, idx: idx}, nil
+	case 2:
+		v2r, err := carv2.NewReader(backing)
+		if err != nil {
+			return nil, err
+		}
+		if idx == nil {
+			if v2r.Header.HasIndex() {
+				idx, err = index.ReadFrom(v2r.IndexReader())
+				if err != nil {
+					return nil, err
+				}
+			} else if idx, err = index.Generate(backing); err != nil {
+				return nil, err
+			}
+		}
+		return &ReadOnly{backing: v2r.CarV1Reader(), idx: idx}, nil
+	default:
+		return nil, fmt.Errorf("unsupported car version: %v", version)
+	}
 }
 
 // OpenReadOnly opens a read-only blockstore from a CAR v2 file, generating an index if it does not exist.
diff --git a/ipld/car/v2/blockstore/readwrite.go b/ipld/car/v2/blockstore/readwrite.go
index 99fd11d2a..cf10a7750 100644
--- a/ipld/car/v2/blockstore/readwrite.go
+++ b/ipld/car/v2/blockstore/readwrite.go
@@ -88,7 +88,7 @@ func NewReadWrite(path string, roots []cid.Cid, opts ...Option) (*ReadWrite, err
 	}
 	b.carV1Writer = internalio.NewOffsetWriter(f, int64(b.header.CarV1Offset))
 	carV1Reader := internalio.NewOffsetReader(f, int64(b.header.CarV1Offset))
-	b.ReadOnly = *ReadOnlyOf(carV1Reader, idx)
+	b.ReadOnly = ReadOnly{backing: carV1Reader, idx: idx}
 	if _, err := f.WriteAt(carv2.Pragma, 0); err != nil {
 		return nil, err
 	}