diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6d20bd7f4391..b091dc462716 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -38,6 +38,7 @@
 
 * `[docs]` Describe the order of execution of describe and test blocks.
   ([#5217](https://github.com/facebook/jest/pull/5217), [#5238](https://github.com/facebook/jest/pull/5238))
+* `[docs]` Add a note on `moduleNameMapper` ordering. ([#5249](https://github.com/facebook/jest/pull/5249))
 
 ## jest 22.0.4
 
diff --git a/docs/Configuration.md b/docs/Configuration.md
index 2c5cf6fb52b4..5641f487e6b4 100644
--- a/docs/Configuration.md
+++ b/docs/Configuration.md
@@ -386,6 +386,9 @@ Example:
 }
 ```
 
+The order in which the mappings are defined matters. Patterns are checked one
+by one until one fits. The most specific rule should be listed first.
+
 _Note: If you provide module name without boundaries `^$` it may cause hard to
 spot errors. E.g. `relay` will replace all modules which contain `relay` as a
 substring in its name: `relay`, `react-relay` and `graphql-relay` will all be