diff --git a/daemon/util/NString.cpp b/daemon/util/NString.cpp
index df41ec70f..5b72ac10a 100644
--- a/daemon/util/NString.cpp
+++ b/daemon/util/NString.cpp
@@ -164,7 +164,7 @@ void CString::AppendFmtV(const char* format, va_list ap)
 
 	m_data = newData;
 
-	vsnprintf(m_data + curLen, newLen + 1, format, ap2);
+	vsnprintf(m_data + curLen, addLen + 1, format, ap2);
 
 	va_end(ap2);
 }