diff --git a/packages/grpc-native-core/index.d.ts b/packages/grpc-native-core/index.d.ts
index 86b76718..247970eb 100644
--- a/packages/grpc-native-core/index.d.ts
+++ b/packages/grpc-native-core/index.d.ts
@@ -794,13 +794,17 @@ declare module "grpc" {
     ERROR,
   }
 
+  export interface Certificate {
+    raw: Buffer;
+  }
+
   /**
    * A callback that will receive the expected hostname and presented peer
    * certificate as parameters. The callback should return an error to
    * indicate that the presented certificate is considered invalid and
    * otherwise returned undefined.
    */
-  export type CheckServerIdentityCallback = (hostname: string, cert: string) => Error | undefined;
+  export type CheckServerIdentityCallback = (hostname: string, cert: Certificate) => Error | undefined;
 
   /**
    * Additional peer verification options that can be set when creating