diff --git a/reference/filesystem/functions/disk-free-space.xml b/reference/filesystem/functions/disk-free-space.xml
index ba936d5398..32b1a1b6b6 100644
--- a/reference/filesystem/functions/disk-free-space.xml
+++ b/reference/filesystem/functions/disk-free-space.xml
@@ -45,7 +45,8 @@
&reftitle.returnvalues;
- Returns the number of available bytes as a float.
+ Returns the number of available bytes as a float
+ or &false; in case of an error.
diff --git a/reference/filesystem/functions/disk-total-space.xml b/reference/filesystem/functions/disk-total-space.xml
index 0a4b8a5943..8c3d138505 100644
--- a/reference/filesystem/functions/disk-total-space.xml
+++ b/reference/filesystem/functions/disk-total-space.xml
@@ -37,7 +37,8 @@
&reftitle.returnvalues;
- Returns the total number of bytes as a float.
+ Returns the total number of bytes as a float
+ or &false; in case of an error.