diff --git a/api/docker/Dockerfile b/api/docker/Dockerfile
index fdd4710f904..3138eb6381b 100644
--- a/api/docker/Dockerfile
+++ b/api/docker/Dockerfile
@@ -14,9 +14,7 @@ FROM php:8.4.5-apache-bookworm AS base
 #Install required php extensions
 RUN apt-get update && \
     apt-get -y install libicu-dev libyaml-dev libzip-dev zip && \
-    pecl install yaml && \
     docker-php-ext-configure intl && \
-    docker-php-ext-enable yaml && \
     docker-php-ext-install intl zip && \
     a2enmod rewrite && a2enmod actions
 
diff --git a/api/docker/DockerfileDemo b/api/docker/DockerfileDemo
index 81ea364554f..5e922d1ff58 100644
--- a/api/docker/DockerfileDemo
+++ b/api/docker/DockerfileDemo
@@ -16,9 +16,7 @@ FROM php:8.4.5-apache-bookworm AS base
 #Install required php extensions
 RUN apt-get update && \
     apt-get -y install libicu-dev libyaml-dev libzip-dev zip && \
-    pecl install yaml && \
     docker-php-ext-configure intl && \
-    docker-php-ext-enable yaml && \
     docker-php-ext-install intl zip && \
     a2enmod rewrite && a2enmod actions
 
diff --git a/environment.xml b/environment.xml
index 5fcc95719dc..2d252a6031b 100644
--- a/environment.xml
+++ b/environment.xml
@@ -2,17 +2,13 @@
 <COMPATIBILITY_MATRIX>
      <PLUGIN name="qtype_stack">
         <PHP version="8.1.0" level="required">
-        <PHP_EXTENSIONS>
-             <PHP_EXTENSION name="mbstring" level="required">
-                 <FEEDBACK>
-                     <ON_ERROR message="mbstringrequired" plugin="qtype_stack" />
-                 </FEEDBACK>
-             </PHP_EXTENSION>
-             <PHP_EXTENSION name="yaml" level="optional">
-                 <FEEDBACK>
-                     <ON_CHECK message="yamlrecommended" plugin="qtype_stack" />
-                 </FEEDBACK>
-             </PHP_EXTENSION>
+            <PHP_EXTENSIONS>
+                 <PHP_EXTENSION name="mbstring" level="required">
+                     <FEEDBACK>
+                         <ON_ERROR message="mbstringrequired" plugin="qtype_stack" />
+                     </FEEDBACK>
+                 </PHP_EXTENSION>
+            </PHP_EXTENSIONS>
          </PHP>
      </PLUGIN>
 </COMPATIBILITY_MATRIX>
diff --git a/lang/en/qtype_stack.php b/lang/en/qtype_stack.php
index a65bafca88e..306eaa31ff1 100644
--- a/lang/en/qtype_stack.php
+++ b/lang/en/qtype_stack.php
@@ -34,7 +34,6 @@
 $string['cachedef_librarycache'] = 'STACK question library renders and file structure';
 
 $string['mbstringrequired'] = 'Installing the MBSTRING library is required for STACK.';
-$string['yamlrecommended']  = 'Installing the YAML library is recommended for STACK.';
 
 // General strings.
 $string['errors']            = 'Errors';