diff --git a/cache/classes/factory.php b/cache/classes/factory.php
index 6ae461d7181..9abfe0ee0b7 100644
--- a/cache/classes/factory.php
+++ b/cache/classes/factory.php
@@ -335,6 +335,15 @@ class cache_factory {
         return $this->cachesfromdefinitions;
     }
 
+    /**
+     * Gets all adhoc caches that have been used within this request.
+     *
+     * @return cache_store[] Caches currently in use
+     */
+    public function get_adhoc_caches_in_use() {
+        return $this->cachesfromparams;
+    }
+
     /**
      * Creates a cache config instance with the ability to write if required.
      *
diff --git a/cache/classes/helper.php b/cache/classes/helper.php
index f15e2ee8fb5..c2aa399e554 100644
--- a/cache/classes/helper.php
+++ b/cache/classes/helper.php
@@ -484,6 +484,9 @@ class cache_helper {
         foreach ($config->get_all_stores() as $store) {
             self::purge_store($store['name'], $config);
         }
+        foreach ($factory->get_adhoc_caches_in_use() as $cache) {
+            $cache->purge();
+        }
     }
 
     /**
diff --git a/cache/tests/cache_test.php b/cache/tests/cache_test.php
index 0a47e4f9b15..8d04cd18dfa 100644
--- a/cache/tests/cache_test.php
+++ b/cache/tests/cache_test.php
@@ -1730,6 +1730,16 @@ class core_cache_testcase extends advanced_testcase {
         }
     }
 
+    /**
+     * Tests that ad-hoc caches are correctly purged with a purge_all call.
+     */
+    public function test_purge_all_with_adhoc_caches() {
+        $cache = \cache::make_from_params(\cache_store::MODE_REQUEST, 'core_cache', 'test');
+        $cache->set('test', 123);
+        cache_helper::purge_all();
+        $this->assertFalse($cache->get('test'));
+    }
+
     /**
      * Test that the default stores all support searching.
      */