diff --git a/source/reference/configuration-options.txt b/source/reference/configuration-options.txt
index 80151feaeda..6100a314b04 100644
--- a/source/reference/configuration-options.txt
+++ b/source/reference/configuration-options.txt
@@ -46,6 +46,12 @@ Declare all settings in this file using the following form:
    parameters, register as true, if they appear in the configuration
    file, regardless of their value.
 
+.. note::
+
+   Ensure the config file is saved with ASCII encoding. mongod does not
+   support config file with non-ASCII encoding such as UTF-8.
+
+
 Settings
 --------