diff --git a/doc/classes/ProjectSettings.xml b/doc/classes/ProjectSettings.xml
index a9632e4b21d..7a14634c1f2 100644
--- a/doc/classes/ProjectSettings.xml
+++ b/doc/classes/ProjectSettings.xml
@@ -137,7 +137,7 @@
 			<argument index="0" name="file" type="String">
 			</argument>
 			<description>
-				Saves the configuration to a custom file.
+				Saves the configuration to a custom file. The file extension must be [code].godot[/code] (to save in text-based [ConfigFile] format) or [code].binary[/code] (to save in binary format).
 			</description>
 		</method>
 		<method name="set_initial_value">