diff --git a/src/Main/globals.cxx b/src/Main/globals.cxx
index bf7ff48c4..7ab82e16e 100644
--- a/src/Main/globals.cxx
+++ b/src/Main/globals.cxx
@@ -173,6 +173,8 @@ void FGGlobals::set_fg_root (const string &root) {
     tmp.append( "version" );
     if ( ulFileExists( tmp.c_str() ) ) {
         fg_root += "/data";
+        SG_LOG(SG_GENERAL, SG_WARN, "Warning: changing bad FG_ROOT/--fg-root to '"
+                << fg_root << '\'');
     }
 
     // remove /sim/fg-root before writing to prevent hijacking