diff --git a/modules/structs/repo.go b/modules/structs/repo.go
index 25918ce0d4..c0ca75455a 100644
--- a/modules/structs/repo.go
+++ b/modules/structs/repo.go
@@ -151,9 +151,9 @@ type CreateRepoOption struct {
 	// TrustModel of the repository
 	// enum: default,collaborator,committer,collaboratorcommitter
 	TrustModel string `json:"trust_model" binding:"In(default,collaborator,committer,collaboratorcommitter)"`
-	// ObjectFormatName of the underlying git repository
+	// ObjectFormatName of the underlying git repository, empty string for default (sha1)
 	// enum: sha1,sha256
-	ObjectFormatName string `json:"object_format_name" binding:"MaxSize(6) In(sha1,sha256)"`
+	ObjectFormatName string `json:"object_format_name" binding:"MaxSize(6)"`
 }
 
 // EditRepoOption options when editing a repository's properties
diff --git a/services/forms/repo_form.go b/services/forms/repo_form.go
index bfd7eb96b5..6dff83f4d2 100644
--- a/services/forms/repo_form.go
+++ b/services/forms/repo_form.go
@@ -42,7 +42,7 @@ type CreateRepoForm struct {
 	ProtectedBranch bool
 
 	ForkSingleBranch string `binding:"MaxSize(255)"`
-	ObjectFormatName string `binding:"MaxSize(6) In(sha1,sha256)"`
+	ObjectFormatName string `binding:"In(sha1,sha256)"`
 }
 
 // Validate validates the fields