This patch adds a check for a null pointer
--- src/header_tag.cpp
+++ src/header_tag.cpp
@@ -54,7 +54,7 @@
 {
   size_t bytesUsed = ID3_TagHeader::SIZE;
 
-  if (_info->is_extended)
+  if (_info && _info->is_extended)
   {
     bytesUsed += _info->extended_bytes;
   }
