diff --git a/src/stream_wrap.cc b/src/stream_wrap.cc
index 7a5e84b567..4eea7c9239 100644
--- a/src/stream_wrap.cc
+++ b/src/stream_wrap.cc
@@ -337,7 +337,7 @@ Handle<Value> StreamWrap::WriteStringImpl(const Arguments& args) {
       break;
 
     case kUcs2:
-      storage_size += string->Length() * sizeof(uint16_t);
+      storage_size = string->Length() * sizeof(uint16_t);
       break;
 
     default: