diff --git a/Makefile b/Makefile
index 2623cc780af21d1d2251be80e813486ae5681604..8bf123000160fd65bcbd3455f67d536825f33081 100644
--- a/Makefile
+++ b/Makefile
@@ -8,7 +8,7 @@ all: Makefile.coq
 
 clean: Makefile.coq
 	+@make -f Makefile.coq clean
-	find theories $$(test -d tests && echo tests) \( -name "*.d" -o -name "*.vo" -o -name "*.aux" -o -name "*.cache" -o -name "*.glob" -o -name "*.vio" \) -print -delete
+	find theories tests \( -name "*.d" -o -name "*.vo" -o -name "*.aux" -o -name "*.cache" -o -name "*.glob" -o -name "*.vio" \) -print -delete || true
 	rm -f Makefile.coq
 .PHONY: clean