diff --git a/README.md b/README.md
index c96c0db5ce..bc49d919f5 100644
--- a/README.md
+++ b/README.md
@@ -82,5 +82,7 @@ Slic3r is licensed under the GNU Affero General Public License, version 3. Slic3
 
 The GNU Affero General Public License, version 3 ensures that if you use any part of this software in any way (even behind a web server), your software must be released under the same license.
 
+Orca Slicer includes a pressure advance calibration pattern test adapted from Andrew Ellis' generator, which is licensed under GNU General Public License, version 3. Ellis' generator is itself adapted from a generator developed by Sineos for Marlin, which is licensed under GNU General Public License, version 3.
+
 The bambu networking plugin is based on non-free libraries. It is optional to the Orca Slicer and provides extended functionalities for users.