diff --git a/lib/Slic3r.pm b/lib/Slic3r.pm
index d317f2e67..98972d7ef 100644
--- a/lib/Slic3r.pm
+++ b/lib/Slic3r.pm
@@ -160,4 +160,8 @@ sub open {
     return CORE::open $$fh, $mode, encode_path($filename);
 }
 
+# this package declaration prevents an ugly fatal warning to be emitted when
+# spawning a new thread
+package GLUquadricObjPtr;
+
 1;