diff --git a/src/main/java/zzzank/probejs/lang/typescript/code/type/js/JSLambdaType.java b/src/main/java/zzzank/probejs/lang/typescript/code/type/js/JSLambdaType.java
index b104da41..e3ac2fc5 100644
--- a/src/main/java/zzzank/probejs/lang/typescript/code/type/js/JSLambdaType.java
+++ b/src/main/java/zzzank/probejs/lang/typescript/code/type/js/JSLambdaType.java
@@ -33,9 +33,13 @@ public List<String> format(Declaration declaration, FormatType formatType) {
         // (arg0: type, arg1: type...) => returnType
         return Collections.singletonList(String.format(
             "(%s => %s)",
-            ParamDecl.formatParams(params, declaration, formatType),
-            //formatType for return should be flipped, to provide better support for type wrapper
-            returnType.line(declaration, formatType == FormatType.INPUT ? FormatType.RETURN : FormatType.INPUT)
+            //when formatType is INPUT, aka this lambda is a param itself, params of this lambda should be concrete
+            ParamDecl.formatParams(
+                params,
+                declaration,
+                formatType == FormatType.INPUT ? FormatType.RETURN : FormatType.INPUT
+            ),
+            returnType.line(declaration, formatType)
         ));
     }