diff --git a/doc/api/os.md b/doc/api/os.md
index 3f11ed65e5f163..5c55f2b7cde353 100644
--- a/doc/api/os.md
+++ b/doc/api/os.md
@@ -142,6 +142,9 @@ The properties included on each object include:
 `nice` values are POSIX-only. On Windows, the `nice` values of all processors
 are always 0.
 
+On Linux and Android when `/proc` filesystem is not accessible, this function 
+may return an empty list.
+
 `os.cpus().length` should not be used to calculate the amount of parallelism
 available to an application. Use
 [`os.availableParallelism()`](#osavailableparallelism) for this purpose.