diff --git a/.gitignore b/.gitignore
index acfdead..d9f7b9c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -16,3 +16,6 @@ Cargo.lock
 
 # MSVC Windows builds of rustc generate these, which store debugging information
 *.pdb
+
+mutants.out/
+mutants.out.old/