diff --git a/service_map.go b/service_map.go
index 1d34844..abe6d8f 100644
--- a/service_map.go
+++ b/service_map.go
@@ -93,7 +93,7 @@ Loop:
 		mCount := mtype.NumIn()
 		if 0 < mCount {
 			paramTypes = make([]reflect.Type, mCount)
-			for indexI := 0; indexI < mCount; indexI++ {
+			for indexI := 1; indexI < mCount; indexI++ {
 				param := mtype.In(indexI)
 				if !isExportedOrBuiltin(param) {
 					continue Loop