diff --git a/README.md b/README.md
index c7cfab1..24ffb20 100644
--- a/README.md
+++ b/README.md
@@ -643,6 +643,8 @@ if err != nil {
 }
 ```
 
+Viper uses [github.com/mitchellh/mapstructure](https://github.com/mitchellh/mapstructure) under the hood for unmarshaling values which uses `mapstructure` tags by default.
+
 ### Marshalling to string
 
 You may need to marshal all the settings held in viper into a string rather than write them to a file.