diff --git a/tinyxml2.cpp b/tinyxml2.cpp
index c4ea7cd..df49d0d 100755
--- a/tinyxml2.cpp
+++ b/tinyxml2.cpp
@@ -1954,6 +1954,7 @@
         SetError( XML_ERROR_FILE_READ_ERROR, 0, 0 );
         return _errorID;
     }
+    TIXMLASSERT( filelength >= 0 );
 
     if ( !LongFitsIntoSizeTMinusOne<>::Fits( filelength ) ) {
         // Cannot handle files which won't fit in buffer together with null terminator