diff --git a/.gitignore b/.gitignore
index 7fdb280335e4..8b2360016d31 100644
--- a/.gitignore
+++ b/.gitignore
@@ -23,6 +23,8 @@ ID
 
 # Emacs directory variable files.
 **/.dir-locals.el
+# Emacs project sentinel files.
+**/.projectile
 
 # User files that may appear at the root
 /.mozconfig*
diff --git a/.hgignore b/.hgignore
index 5ef1290e1a35..db437c6a9bee 100644
--- a/.hgignore
+++ b/.hgignore
@@ -20,6 +20,8 @@ compile_commands\.json
 
 # Emacs directory variable files.
 \.dir-locals\.el
+# Emacs project sentinel files.
+\.projectile
 
 # User files that may appear at the root
 ^\.mozconfig