diff --git a/mkvmuxerutil.cpp b/mkvmuxerutil.cpp
index 96350e9..18060e9 100644
--- a/mkvmuxerutil.cpp
+++ b/mkvmuxerutil.cpp
@@ -292,11 +292,11 @@ bool WriteEbmlElement(IMkvWriter* writer, uint64 type, const char* value) {
   if (WriteID(writer, type))
     return false;
 
-  const int32 length = strlen(value);
+  const uint64 length = strlen(value);
   if (WriteUInt(writer, length))
     return false;
 
-  if (writer->Write(value, length))
+  if (writer->Write(value, static_cast<const uint32>(length)))
     return false;
 
   return true;