diff --git a/system/Files/File.php b/system/Files/File.php
index 02c8f181b19b..15b53262e9c2 100644
--- a/system/Files/File.php
+++ b/system/Files/File.php
@@ -59,7 +59,8 @@ public function __construct(string $path, bool $checkFile = false)
      *
      * Implementations SHOULD return the value stored in the "size" key of
      * the file in the $_FILES array if available, as PHP calculates this based
-     * on the actual size transmitted.
+     * on the actual size transmitted. A RuntimeException will be thrown if the file
+     * does not exist or an error occurs.
      *
      * @return false|int The file size in bytes, or false on failure
      */
diff --git a/user_guide_src/source/libraries/files.rst b/user_guide_src/source/libraries/files.rst
index 0b55982692c2..8d2e90c9df46 100644
--- a/user_guide_src/source/libraries/files.rst
+++ b/user_guide_src/source/libraries/files.rst
@@ -46,6 +46,8 @@ Returns the size of the uploaded file in bytes:
 
 .. literalinclude:: files/004.php
 
+A ``RuntimeException`` will be thrown if the file does not exist or an error occurs.
+
 getSizeByUnit()
 ===============
 
@@ -54,6 +56,8 @@ the results in kilobytes or megabytes, respectively:
 
 .. literalinclude:: files/005.php
 
+A ``RuntimeException`` will be thrown if the file does not exist or an error occurs.
+
 getMimeType()
 =============