diff --git a/doc/environments/groupthm/Makefile b/doc/environments/groupthm/Makefile
index 7c7ee70..656b681 100644
--- a/doc/environments/groupthm/Makefile
+++ b/doc/environments/groupthm/Makefile
@@ -16,5 +16,6 @@ clean: clean-sty
 
 clean-sty:
 	rm -f groupthm.sty
+	rm -f groupthm.tdo
 
 .PHONY: pdf clean