diff --git a/.github/workflows/phpmd.yml b/.github/workflows/phpmd.yml
index 7e9af23..8f61d3e 100644
--- a/.github/workflows/phpmd.yml
+++ b/.github/workflows/phpmd.yml
@@ -47,7 +47,7 @@ jobs:
           tools: phpmd
 
       - name: Run PHPMD
-        run: phpmd . sarif codesize --reportfile phpmd-results.sarif
+        run: phpmd --ignore-violations-on-exit . sarif phpmd.ruleset.xml --reportfile phpmd-results.sarif
         continue-on-error: true
 
       - name: Upload analysis results to GitHub
diff --git a/composer.json b/composer.json
index 8f46bec..384df3c 100644
--- a/composer.json
+++ b/composer.json
@@ -25,7 +25,8 @@
     "scripts": {
         "phpcs": "phpcs",
         "phpstan": "phpstan analyse",
-        "phpunit": "phpunit"
+        "phpunit": "phpunit",
+        "phpmd": "phpmd src,tests ansi phpmd.ruleset.xml"
     },
     "require": {
         "php": "^7.3 || ^8.0",
@@ -34,6 +35,7 @@
     "require-dev": {
         "httpwg/structured-field-tests": "*@dev",
         "paragonie/constant_time_encoding": "^2.6.3",
+        "phpmd/phpmd": "^2.15",
         "phpstan/phpstan": "^1.9",
         "phpstan/phpstan-phpunit": "^1.3",
         "phpunit/phpunit": "^9.5.27",
diff --git a/phpmd.ruleset.xml b/phpmd.ruleset.xml
new file mode 100644
index 0000000..3a24322
--- /dev/null
+++ b/phpmd.ruleset.xml
@@ -0,0 +1,13 @@
+<?xml version="1.0"?>
+<ruleset name="PHPMD Ruleset"
+         xmlns="http://pmd.sf.net/ruleset/1.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://pmd.sf.net/ruleset/1.0.0
+                     http://pmd.sf.net/ruleset_xml_schema.xsd"
+         xsi:noNamespaceSchemaLocation="
+                     http://pmd.sf.net/ruleset_xml_schema.xsd">
+    <description>PHPMD Ruleset</description>
+
+    <rule ref="rulesets/codesize.xml"/>
+    <rule ref="rulesets/unusedcode.xml"/>
+</ruleset>
diff --git a/src/Parser.php b/src/Parser.php
index 2662761..13a59f5 100644
--- a/src/Parser.php
+++ b/src/Parser.php
@@ -4,6 +4,9 @@
 
 namespace gapple\StructuredFields;
 
+/**
+ * @SuppressWarnings(PHPMD.ExcessiveClassComplexity)
+ */
 class Parser
 {
     public static function parseDictionary(string $string): Dictionary
@@ -276,6 +279,9 @@ private static function parseString(string &$string): string
         throw new ParseException("Invalid end of string");
     }
 
+    /**
+     * @SuppressWarnings(PHPMD.CyclomaticComplexity)
+     */
     private static function parseDisplayString(string &$string): DisplayString
     {
         if (strpos($string, '%"') !== 0) {
diff --git a/src/Serializer.php b/src/Serializer.php
index a3438b0..8c126ae 100644
--- a/src/Serializer.php
+++ b/src/Serializer.php
@@ -4,6 +4,9 @@
 
 namespace gapple\StructuredFields;
 
+/**
+ * @SuppressWarnings(PHPMD.ExcessiveClassComplexity)
+ */
 class Serializer
 {
     /**
@@ -145,6 +148,8 @@ private static function serializeInnerList(array $value, ?object $parameters = n
 
     /**
      * @param mixed $value
+     *
+     * @SuppressWarnings(PHPMD.CyclomaticComplexity)
      */
     private static function serializeBareItem($value): string
     {
diff --git a/tests/Httpwg/HttpwgTest.php b/tests/Httpwg/HttpwgTest.php
index 78a675d..bea80a0 100644
--- a/tests/Httpwg/HttpwgTest.php
+++ b/tests/Httpwg/HttpwgTest.php
@@ -29,6 +29,9 @@ abstract class HttpwgTest extends RulesetTest
      */
     protected $ruleset;
 
+    /**
+     * @SuppressWarnings(PHPMD.CyclomaticComplexity)
+     */
     protected function rulesetDataProvider(): array
     {
         $path = __DIR__ . '/../../vendor/httpwg/structured-field-tests/' . $this->ruleset . '.json';