diff --git a/stack/cas/parsingrules/601_castext.filter.php b/stack/cas/parsingrules/601_castext.filter.php
index ba6a45a012a..e1ca512deb7 100644
--- a/stack/cas/parsingrules/601_castext.filter.php
+++ b/stack/cas/parsingrules/601_castext.filter.php
@@ -91,6 +91,13 @@ public function filter(MP_Node $ast, array &$errors, array &$answernotes, stack_
                         $compiled = $compiled->statement;
                     }
                     $compiled->position['castext'] = true;
+                    if ($compiled instanceof MP_String) {
+                        // An inline-CASText fragment cannot be flat, as injections of such could not be distinguished
+                        // from string injections. For this reason we tag it with a marker to stop simplification.
+                        // And make it non flat if it already is.
+                        $compiled = new MP_List([new MP_String('%root'), $compiled]);
+                    }
+                    $compiled->position['inline-castext'] = true;
                     $node->parentnode->replace($node, $compiled);
                     return false;
                 } else if ($node->name instanceof MP_Identifier && $node->name->value === 'castext_concat') {
diff --git a/stack/cas/parsingrules/602_castext_simplifier.filter.php b/stack/cas/parsingrules/602_castext_simplifier.filter.php
index 892d9ecacaa..f55572d6408 100644
--- a/stack/cas/parsingrules/602_castext_simplifier.filter.php
+++ b/stack/cas/parsingrules/602_castext_simplifier.filter.php
@@ -237,8 +237,8 @@ public function filter(MP_Node $ast, array &$errors, array &$answernotes, stack_
                         $node->items[0]->value === 'demoodle' ||
                         $node->items[0]->value === 'htmlformat')
                 ) {
-                    if ($node->items[0]->value === '%root' && count($node->items) === 2 && $node->items[1] instanceof MP_String) {
-                        // A concatenation of a single string, can be removed. If %root.
+                    if ($node->items[0]->value === '%root' && count($node->items) === 2 && $node->items[1] instanceof MP_String && !(isset($node->position['inline-castext']) && $node->position['inline-castext'])) {
+                        // A concatenation of a single string, can be removed. If %root and not inline-CASText.
                         $node->parentnode->replace($node, $node->items[1]);
                         return false;
                     }