diff --git a/engine/userguide/storagedriver/overlayfs-driver.md b/engine/userguide/storagedriver/overlayfs-driver.md
index 3433933938..186cf6c0be 100644
--- a/engine/userguide/storagedriver/overlayfs-driver.md
+++ b/engine/userguide/storagedriver/overlayfs-driver.md
@@ -129,7 +129,7 @@ If you are still using the `overlay` driver rather than `overlay2`, see
 
 OverlayFS layers two directories on a single Linux host and presents them as
 a single directory. These directories are called _layers_ and the unification
-process is referred to a a _union mount_. OverlayFS refers to the lower directory
+process is referred to as a _union mount_. OverlayFS refers to the lower directory
 as `lowerdir` and the upper directory a `upperdir`. The unified view is exposed
 through its own directory called `merged`.