diff --git a/Utility b/Utility
index 627ced70..575aff86 160000
--- a/Utility
+++ b/Utility
@@ -1 +1 @@
-Subproject commit 627ced700e866d8c36a6c904347a18368db7565c
+Subproject commit 575aff86cc7463193671542e6adad565c2437c6e
diff --git a/src/main/resources/TLLogWriter.v b/src/main/resources/TLLogWriter.v
index e9f5a8f9..a199fd7c 100644
--- a/src/main/resources/TLLogWriter.v
+++ b/src/main/resources/TLLogWriter.v
@@ -31,7 +31,7 @@ module TLLogWriter(
     input clock,
     input reset
 );
-    parameter string prefix;
+    parameter string prefix = "undefined";
 
     always @(posedge clock) begin
         if(wen && !reset) begin
diff --git a/src/main/scala/huancun/debug/DirectoryLogger.scala b/src/main/scala/huancun/debug/DirectoryLogger.scala
index c8c541f8..3e814e4f 100644
--- a/src/main/scala/huancun/debug/DirectoryLogger.scala
+++ b/src/main/scala/huancun/debug/DirectoryLogger.scala
@@ -62,7 +62,7 @@ class DirLogWriter(prefix: String)
       |    input clock,
       |    input reset
       |);
-      |    parameter string prefix;
+      |    parameter string prefix = "undefined";
       |
       |    always @(posedge clock) begin
       |        if(wen && !reset) begin