diff --git a/doc/api/os.md b/doc/api/os.md
index 820c6992ae8e4f..31566d02490fb4 100644
--- a/doc/api/os.md
+++ b/doc/api/os.md
@@ -74,6 +74,8 @@ added: v0.3.3
 * Returns: {Object\[]}
 
 Returns an array of objects containing information about each logical CPU core.
+The array will be empty if no CPU information is available, such as if the
+`/proc` file system is unavailable.
 
 The properties included on each object include: