diff --git a/verifiable/did_doc.go b/verifiable/did_doc.go
index ff6b3ee..8fb63b2 100644
--- a/verifiable/did_doc.go
+++ b/verifiable/did_doc.go
@@ -138,8 +138,8 @@ type GistInfo struct {
 
 // GistInfoProof representation proof of GistInfo object.
 type GistInfoProof struct {
-	Type string `json:"type"`
 	merkletree.Proof
+	Type ProofType `json:"type"`
 }
 
 // IdentityState representation all info about identity.