diff --git a/lib/utils.js b/lib/utils.js
index 7ffa7b6..9593728 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -4,15 +4,15 @@ const METHOD_PROPS = ['name', 'options', 'type', 'requestStream', 'responseStrea
   'requestName', 'responseName', 'path', 'requestType', 'responseType', 'originalName']
 
 function getCallTypeFromCall (call) {
-  const name = Object.getPrototypeOf(call).constructor.name
+  const handlerType = call && call.call && call.call.handler && call.call.handler.type
 
-  if (name.indexOf('ServerUnaryCall') === 0) {
+  if (handlerType === 'unary') {
     return CallType.UNARY
-  } else if (name.indexOf('ServerWritableStream') === 0) {
+  } else if (handlerType === 'serverStream') {
     return CallType.RESPONSE_STREAM
-  } else if (name.indexOf('ServerReadableStream') === 0) {
+  } else if (handlerType === 'clientStream') {
     return CallType.REQUEST_STREAM
-  } else if (name.indexOf('ServerDuplexStream') === 0) {
+  } else if (handlerType === 'bidi') {
     return CallType.DUPLEX
   }
 }