diff --git a/.upgradenotes/MDL-86311-2025081418402045.yml b/.upgradenotes/MDL-86311-2025081418402045.yml
new file mode 100644
index 00000000000..3b86b7cea70
--- /dev/null
+++ b/.upgradenotes/MDL-86311-2025081418402045.yml
@@ -0,0 +1,13 @@
+issueNumber: MDL-86311
+notes:
+  core:
+    - message: >-
+        The default PHPUnit configuration now enables the following properties,
+        ensuring PHP warnings will cause test failures (restoring pre-PHPUnit
+        version 10 behaviour):
+
+
+        * `failOnDeprecation`
+
+        * `failOnWarning`
+      type: changed
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index f0ecc67bd16..90b9dea5f03 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -6,6 +6,8 @@
   processIsolation="false"
   backupGlobals="false"
   cacheResult="false"
+  failOnDeprecation="true"
+  failOnWarning="true"
   stopOnError="false"
   stopOnFailure="false"
   stopOnIncomplete="false"