diff --git a/packages/ethereum-types/src/index.ts b/packages/ethereum-types/src/index.ts
index 31c4f42df5..45a288fe13 100644
--- a/packages/ethereum-types/src/index.ts
+++ b/packages/ethereum-types/src/index.ts
@@ -29,8 +29,8 @@ export interface ZeroExProvider {
     isZeroExProvider?: boolean;
     isMetaMask?: boolean;
     isParity?: boolean;
-    stop?: () => void;
-    enable?: () => Promise<void>;
+    stop?(): void;
+    enable?(): Promise<void>;
     sendAsync(payload: JSONRPCRequestPayload, callback: JSONRPCErrorCallback): void;
 }