diff --git a/mysql-test/main/xml.result b/mysql-test/main/xml.result
index d0b1d1782a1..a960d8cc316 100644
--- a/mysql-test/main/xml.result
+++ b/mysql-test/main/xml.result
@@ -1320,5 +1320,17 @@ f
 foo
 <b></b>
 #
-# Start of 10.5 tests
+# End of 10.5 tests
 #
+# Start of 11.4 tests
+#
+# MDEV-36565 Assertion `src != ((void *)0)' failed in my_casedn_8bit
+#
+SET NAMES latin1;
+SELECT  lcase((extractvalue('a', 'a'))) a FROM (select 1) dt;
+a
+
+SELECT  ucase((extractvalue('a', 'a'))) a FROM (select 1) dt;
+a
+
+# End of 11.4 tests
diff --git a/mysql-test/main/xml.test b/mysql-test/main/xml.test
index 2d0dd9907bb..e0954c5f6bb 100644
--- a/mysql-test/main/xml.test
+++ b/mysql-test/main/xml.test
@@ -822,5 +822,17 @@ DROP TABLE t1;
 SELECT 'foo' AS f UNION SELECT BINARY( UpdateXML('<a></a>', '/a', '<b></b>')) AS f;
 
 --echo #
---echo # Start of 10.5 tests
+--echo # End of 10.5 tests
 --echo #
+
+--echo # Start of 11.4 tests
+
+--echo #
+--echo # MDEV-36565 Assertion `src != ((void *)0)' failed in my_casedn_8bit
+--echo #
+
+SET NAMES latin1;
+SELECT  lcase((extractvalue('a', 'a'))) a FROM (select 1) dt;
+SELECT  ucase((extractvalue('a', 'a'))) a FROM (select 1) dt;
+
+--echo # End of 11.4 tests
diff --git a/sql/item_xmlfunc.cc b/sql/item_xmlfunc.cc
index 02c37b45d8f..86c4e423947 100644
--- a/sql/item_xmlfunc.cc
+++ b/sql/item_xmlfunc.cc
@@ -176,8 +176,8 @@ public:
       }
     }
 
-    str->length(0);
-    str->set_charset(collation.collation);
+    // Make sure we never return {Ptr=nullptr, str_length=0}
+    str->copy("", 0, collation.collation);
     for (uint i=0 ; i < numnodes; i++)
     {
       if(active[i])