diff --git a/pkg/schema/converter/openapi.go b/pkg/schema/converter/openapi.go
index e2b0124..ae39a5d 100644
--- a/pkg/schema/converter/openapi.go
+++ b/pkg/schema/converter/openapi.go
@@ -107,6 +107,8 @@ func toField(schema proto.Schema) schemas.Field {
 			f.Type = sub.GetPath().String()
 		}
 	case *proto.Arbitrary:
+		logrus.Debugf("arbitrary type: %v", schema)
+		f.Type = "json"
 	default:
 		logrus.Errorf("unknown type: %v", schema)
 		f.Type = "json"