diff --git a/build/build.xml b/build/build.xml
index 9a66853b98..5354b5d48c 100644
--- a/build/build.xml
+++ b/build/build.xml
@@ -87,6 +87,7 @@
 				--standard=build/code_sniffer/ruleset-php-legacy-core.xml
 				--ignore=${project.basedir}/phpBB/cache/*
 				--ignore=${project.basedir}/phpBB/develop/*
+				--ignore=${project.basedir}/phpBB/ext/*
 				--ignore=${project.basedir}/phpBB/includes/diff/*.php
 				--ignore=${project.basedir}/phpBB/includes/sphinxapi.php
 				--ignore=${project.basedir}/phpBB/includes/utf/data/*
@@ -96,10 +97,17 @@
 				--ignore=${project.basedir}/phpBB/vendor/*
 				phpBB"
 			dir="." returnProperty="retval-php-legacy" passthru="true" />
+		<exec command="phpBB/vendor/bin/phpcs
+				-s
+				--extensions=php
+				--standard=build/code_sniffer/ruleset-php-extensions.xml
+				phpBB/ext"
+			dir="." returnProperty="retval-php-ext" passthru="true" />
 		<if>
 			<or>
 				<not><equals arg1="${retval-php-strict}" arg2="0" /></not>
 				<not><equals arg1="${retval-php-legacy}" arg2="0" /></not>
+				<not><equals arg1="${retval-php-ext}" arg2="0" /></not>
 			</or>
 			<then>
 				<fail message="PHP Code Sniffer failed." />
diff --git a/build/code_sniffer/ruleset-php-extensions.xml b/build/code_sniffer/ruleset-php-extensions.xml
new file mode 100644
index 0000000000..2d388103c3
--- /dev/null
+++ b/build/code_sniffer/ruleset-php-extensions.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0"?>
+<ruleset name="phpBB PHP Strict Standard Extensions">
+
+ <description>phpBB coding standard for PHP files of phpBB extensions</description>
+
+ <rule ref="./ruleset-php-strict.xml" />
+
+</ruleset>