diff --git a/lib/autoInject.js b/lib/autoInject.js
index b1f242e18..68eb3c99c 100644
--- a/lib/autoInject.js
+++ b/lib/autoInject.js
@@ -2,8 +2,8 @@ import auto from './auto.js'
 import wrapAsync from './internal/wrapAsync.js'
 import { isAsync } from './internal/wrapAsync.js'
 
-var FN_ARGS = /^(?:async\s+)?(?:function)?\s*\w*\s*\(\s*([^)]+)\s*\)(?:\s*{)/;
-var ARROW_FN_ARGS = /^(?:async\s+)?\(?\s*([^)=]+)\s*\)?(?:\s*=>)/;
+var FN_ARGS = /^(?:async\s)?(?:function)?\s*(?:\w+\s*)?\(([^)]+)\)(?:\s*{)/;
+var ARROW_FN_ARGS = /^(?:async\s)?\s*(?:\(\s*)?((?:[^)=\s]\s*)*)(?:\)\s*)?=>/;
 var FN_ARG_SPLIT = /,/;
 var FN_ARG = /(=.+)?(\s*)$/;