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 @@
  <refsect1 role="returnvalues">
   &reftitle.returnvalues;
   <para>
-   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.
   </para>
  </refsect1>
 
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 @@
  <refsect1 role="returnvalues">
   &reftitle.returnvalues;
   <para>
-   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.
   </para>
  </refsect1>