diff --git a/sim/Makefile b/sim/Makefile
index 09d417124..79a3042e4 100644
--- a/sim/Makefile
+++ b/sim/Makefile
@@ -62,6 +62,7 @@ coveragetests:
 	make -C ../tests/coverage/ --jobs
 
 deriv:
+	rm -rf ../config/deriv
 	derivgen.pl
 
 benchmarks: