diff --git a/HISTORY.md b/HISTORY.md
index 77e14248e3..41caf41c76 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -35,6 +35,9 @@
 
   * Add `kmeans_max_iterations` option to GMM training binding `gmm_train_main`.
 
+  * Bump minimum Armadillo version to 8.400.0 due to ensmallen dependency
+    requirement (#2015).
+
 ### mlpack 3.1.1
 ###### 2019-05-26
   * Fix random forest bug for numerical-only data (#1887).