diff --git a/CHANGELOG.md b/CHANGELOG.md
index e260aeb42..60dc05742 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,8 @@
     * Fixed `bin/gpm uninstall` script not working because of bad typehint [#3172](https://github.com/getgrav/grav/issues/3172)
     * Fixed `login: visibility_requires_access` not working in pages [#3176](https://github.com/getgrav/grav/issues/3176)
     * Fixed cannot change image format [#3173](https://github.com/getgrav/grav/issues/3173)
+    * Fixed saving page in expert mode [#3174](https://github.com/getgrav/grav/issues/3174)
+    * Fixed exception in `$flexPage->frontmatter()` method when setting value
 
 # v1.7.3
 ## 01/21/2021
diff --git a/system/src/Grav/Framework/Flex/Pages/FlexPageObject.php b/system/src/Grav/Framework/Flex/Pages/FlexPageObject.php
index d3a8330be..af4141599 100644
--- a/system/src/Grav/Framework/Flex/Pages/FlexPageObject.php
+++ b/system/src/Grav/Framework/Flex/Pages/FlexPageObject.php
@@ -396,7 +396,7 @@ class FlexPageObject extends FlexObject implements PageInterface, FlexTranslateI
             unset($elements['content']);
         }
 
-        // RAW frontmatter support.
+        // TODO: Remove: RAW frontmatter support has been moved to Flex-Objects v1.0.2 controller.
         if (isset($elements['frontmatter'])) {
             $formatter = new YamlFormatter();
             try {
diff --git a/system/src/Grav/Framework/Flex/Pages/Traits/PageLegacyTrait.php b/system/src/Grav/Framework/Flex/Pages/Traits/PageLegacyTrait.php
index 6d09b2acf..c6a9475d2 100644
--- a/system/src/Grav/Framework/Flex/Pages/Traits/PageLegacyTrait.php
+++ b/system/src/Grav/Framework/Flex/Pages/Traits/PageLegacyTrait.php
@@ -92,8 +92,11 @@ trait PageLegacyTrait
     public function frontmatter($var = null): string
     {
         if (null !== $var) {
-            // TODO:
-            throw new RuntimeException(__METHOD__ . '(string): Not Implemented');
+            $formatter = new YamlFormatter();
+            $this->setProperty('frontmatter', $var);
+            $this->setProperty('header', $formatter->decode($var));
+
+            return $var;
         }
 
         $storage = $this->getFlexDirectory()->getStorage();