diff --git a/README.md b/README.md
index d289d39..e83e002 100644
--- a/README.md
+++ b/README.md
@@ -25,6 +25,11 @@ composer require --dev roave/infection-static-analysis-plugin
 vendor/bin/roave-infection-static-analysis-plugin
 ```
 
+Do not use this tool if your project has a
+[Psalm baseline](https://psalm.dev/docs/running_psalm/dealing_with_code_issues/#using-a-baseline-file) file. In that
+case issues that are ignored due to being present in the baseline will be reported as killed, spuriously inflating your
+mutation score indicator. See [issue #484](https://github.com/Roave/infection-static-analysis-plugin/issues/484).
+
 ### Configuration
 
 The `roave-infection-static-analysis-plugin` binary accepts all of `infection` flags and arguments, and an additional `--psalm-config` argument.
diff --git a/bin/roave-infection-static-analysis-plugin b/bin/roave-infection-static-analysis-plugin
index 5fda677..ff680e7 100755
--- a/bin/roave-infection-static-analysis-plugin
+++ b/bin/roave-infection-static-analysis-plugin
@@ -49,7 +49,7 @@ use function var_export;
         ));
     })();
 
-    require_once $projectPath . '/vendor/autoload.php';
+    require_once __DIR__ . '/../vendor/autoload.php';
 
     if (! defined('PSALM_VERSION')) {
         define('PSALM_VERSION', InstalledVersions::getVersion('vimeo/psalm'));
@@ -65,7 +65,7 @@ use function var_export;
 
     RuntimeCaches::clearAll();
 
-    $configuration = $configuration ?? $projectPath;
+    $configuration ??= $projectPath;
 
     if (is_file($configuration)) {
         $config = Config::loadFromXMLFile($configuration, $projectPath);
diff --git a/composer.json b/composer.json
index ca99fbf..6bf2b82 100644
--- a/composer.json
+++ b/composer.json
@@ -31,7 +31,10 @@
     "autoload-dev": {
         "psr-4": {
             "Roave\\InfectionStaticAnalysisTest\\": "test/unit/Roave/InfectionStaticAnalysisTest"
-        }
+        },
+        "classmap": [
+            "test/asset/ProjectWithPsalmBaseline/src/HelloWorld.php"
+        ]
     },
     "config": {
         "allow-plugins": {
diff --git a/phpcs.xml.dist b/phpcs.xml.dist
index 7d7578d..b4d9cd5 100644
--- a/phpcs.xml.dist
+++ b/phpcs.xml.dist
@@ -13,6 +13,7 @@
 
     <file>src</file>
     <file>test</file>
+    <exclude-pattern>test/asset/ProjectWithPsalmBaseline</exclude-pattern>
 
     <rule ref="Doctrine">
         <!-- properties in psalm config do not use camel-case naming -->
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index e59d8ed..4d31092 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,7 +1,7 @@
 <?xml version="1.0"?>
 <phpunit
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-    xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/10.1/phpunit.xsd"
+    xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd"
     bootstrap="./vendor/autoload.php"
     beStrictAboutChangesToGlobalState="true"
     beStrictAboutCoverageMetadata="true"
diff --git a/psalm.xml b/psalm.xml
index f760fd4..06954e8 100644
--- a/psalm.xml
+++ b/psalm.xml
@@ -5,13 +5,18 @@
     xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd"
     name="Example Psalm config with recommended defaults"
     errorLevel="1"
+    findUnusedBaselineEntry="true"
+    findUnusedCode="true"
 >
     <projectFiles>
-        <directory name="bin"/>
+        <file name="bin/roave-infection-static-analysis-plugin"/>
         <directory name="src"/>
-        <directory name="test"/>
+        <directory name="test/unit"/>
+        <ignoreFiles>
+            <directory name="test/asset/ProjectWithPsalmBaseline/src"/>
+        </ignoreFiles>
     </projectFiles>
-
+    
     <issueHandlers>
         <!--
         we do a loooooooot of kinky stuff with infection's internals: that's by "design",
@@ -60,11 +65,11 @@
             </errorLevel>
         </PropertyNotSetInConstructor>
 
-        <!-- composer/package-versions-deprecated is in use by design -->
-        <DeprecatedClass>
+        <!-- phpunit tests are entry points - they are generally unused -->
+        <UnusedClass>
             <errorLevel type="suppress">
-                <referencedClass name="PackageVersions\Versions"/>
+                <directory name="test"/>
             </errorLevel>
-        </DeprecatedClass>
+        </UnusedClass>
     </issueHandlers>
 </psalm>
diff --git a/src/Roave/InfectionStaticAnalysis/CliUtility.php b/src/Roave/InfectionStaticAnalysis/CliUtility.php
index b6a8b90..c5c041a 100644
--- a/src/Roave/InfectionStaticAnalysis/CliUtility.php
+++ b/src/Roave/InfectionStaticAnalysis/CliUtility.php
@@ -12,12 +12,8 @@
 use function substr;
 
 /** @internal */
-final class CliUtility
+abstract class CliUtility
 {
-    private function __construct()
-    {
-    }
-
     /**
      * @param list<non-empty-string> $arguments
      * @param non-empty-string       $argument
diff --git a/test/asset/ProjectWithPsalmBaseline/infection.json5 b/test/asset/ProjectWithPsalmBaseline/infection.json5
new file mode 100644
index 0000000..ca97ca2
--- /dev/null
+++ b/test/asset/ProjectWithPsalmBaseline/infection.json5
@@ -0,0 +1,11 @@
+{
+    "$schema": "vendor/infection/infection/resources/schema.json",
+    "source": {
+        "directories": [
+            "src"
+        ]
+    },
+    "mutators": {
+        "@default": true
+    }
+}
\ No newline at end of file
diff --git a/test/asset/ProjectWithPsalmBaseline/phpunit b/test/asset/ProjectWithPsalmBaseline/phpunit
new file mode 100755
index 0000000..67c63c6
--- /dev/null
+++ b/test/asset/ProjectWithPsalmBaseline/phpunit
@@ -0,0 +1,11 @@
+#!/usr/bin/env php
+<?php
+/**
+ * This file aliases the PHPUnit binary in the current directory.
+ *
+ * Without a discoverable executable, the `roave/infection-static-analysis`
+ * `bin/roave-infection-static-analysis-plugin` executable will otherwise
+ * fail to start up. It also emulates minimal autoloading.
+ */
+
+require __DIR__ . '/../../../vendor/bin/phpunit';
diff --git a/test/asset/ProjectWithPsalmBaseline/phpunit.xml b/test/asset/ProjectWithPsalmBaseline/phpunit.xml
new file mode 100644
index 0000000..c7c04b5
--- /dev/null
+++ b/test/asset/ProjectWithPsalmBaseline/phpunit.xml
@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="../../../vendor/phpunit/phpunit/phpunit.xsd"
+         cacheResult="false"
+         executionOrder="depends,defects"
+         requireCoverageMetadata="true"
+         beStrictAboutCoverageMetadata="true"
+         beStrictAboutOutputDuringTests="true"
+         failOnRisky="true"
+         failOnWarning="true">
+    <testsuites>
+        <testsuite name="default">
+            <directory>tests</directory>
+        </testsuite>
+    </testsuites>
+
+    <source restrictDeprecations="true" restrictNotices="true" restrictWarnings="true">
+        <include>
+            <directory>src</directory>
+        </include>
+    </source>
+</phpunit>
diff --git a/test/asset/ProjectWithPsalmBaseline/psalm-baseline.xml b/test/asset/ProjectWithPsalmBaseline/psalm-baseline.xml
new file mode 100644
index 0000000..b73d400
--- /dev/null
+++ b/test/asset/ProjectWithPsalmBaseline/psalm-baseline.xml
@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<files psalm-version="5.16.0@2897ba636551a8cb61601cc26f6ccfbba6c36591">
+  <file src="src/HelloWorld.php">
+    <MissingParamType>
+      <code>$mixture</code>
+    </MissingParamType>
+    <MixedInferredReturnType>
+      <code>int</code>
+    </MixedInferredReturnType>
+    <MixedOperand>
+      <code>$mixture</code>
+    </MixedOperand>
+    <MixedReturnStatement>
+      <code>$mixture + 2</code>
+    </MixedReturnStatement>
+  </file>
+</files>
diff --git a/test/asset/ProjectWithPsalmBaseline/psalm.xml b/test/asset/ProjectWithPsalmBaseline/psalm.xml
new file mode 100644
index 0000000..67bae82
--- /dev/null
+++ b/test/asset/ProjectWithPsalmBaseline/psalm.xml
@@ -0,0 +1,15 @@
+<?xml version="1.0"?>
+<psalm
+    errorLevel="1"
+    resolveFromConfigFile="true"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xmlns="https://getpsalm.org/schema/config"
+    xsi:schemaLocation="https://getpsalm.org/schema/config ../../../vendor/vimeo/psalm/config.xsd"
+    findUnusedBaselineEntry="true"
+    findUnusedCode="true"
+    errorBaseline="psalm-baseline.xml"
+>
+    <projectFiles>
+        <directory name="src" />
+    </projectFiles>
+</psalm>
diff --git a/test/asset/ProjectWithPsalmBaseline/src/HelloWorld.php b/test/asset/ProjectWithPsalmBaseline/src/HelloWorld.php
new file mode 100644
index 0000000..86a154b
--- /dev/null
+++ b/test/asset/ProjectWithPsalmBaseline/src/HelloWorld.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace Acme\ProjectWithPsalmBaseline;
+
+/**
+ * @psalm-api
+ */
+class HelloWorld
+{
+    /**
+     * This function has full test coverage, but the test is effectively assertion-free and useless. But
+     * because the function also has Psalm errors that are in the baseline, ISAP will think the test is good
+     * and give us a 100% MSI.
+     */
+    public function takesImplictMixedReturnsIntAndIsCoveredByBaseline($mixture): int
+    {
+        return $mixture + 2;
+    }
+}
\ No newline at end of file
diff --git a/test/asset/ProjectWithPsalmBaseline/tests/HelloWorldTest.php b/test/asset/ProjectWithPsalmBaseline/tests/HelloWorldTest.php
new file mode 100644
index 0000000..57293fc
--- /dev/null
+++ b/test/asset/ProjectWithPsalmBaseline/tests/HelloWorldTest.php
@@ -0,0 +1,17 @@
+<?php
+
+use Acme\ProjectWithPsalmBaseline\HelloWorld;
+
+/**
+ * @covers \Acme\ProjectWithPsalmBaseline\HelloWorld
+ */
+class HelloWorldTest extends \PHPUnit\Framework\TestCase
+{
+    public function testNothingButProvideCoverage(): void
+    {
+        $sut = new HelloWorld();
+        $_resultWeDontCheck = $sut->takesImplictMixedReturnsIntAndIsCoveredByBaseline(3);
+
+        $this->assertSame(4, 2+2);
+    }
+}
\ No newline at end of file
diff --git a/test/unit/Roave/InfectionStaticAnalysisTest/ProjectWithBaselineTest.php b/test/unit/Roave/InfectionStaticAnalysisTest/ProjectWithBaselineTest.php
new file mode 100644
index 0000000..a08dce4
--- /dev/null
+++ b/test/unit/Roave/InfectionStaticAnalysisTest/ProjectWithBaselineTest.php
@@ -0,0 +1,25 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Roave\InfectionStaticAnalysisTest;
+
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\Process\Process;
+
+class ProjectWithBaselineTest extends TestCase
+{
+    public function testItSpuriouslyReportsMutantAsKilledWithPsalmBaseline(): void
+    {
+        $process = new Process([__DIR__ . '/../../../../bin/roave-infection-static-analysis-plugin']);
+        $process->setWorkingDirectory(__DIR__ . '/../../../asset/ProjectWithPsalmBaseline');
+
+        $process->mustRun();
+
+        $output = $process->getOutput();
+
+        $this->assertSame(0, $process->getExitCode());
+        $this->assertStringContainsString('4 mutants were killed', $output);
+        $this->assertStringContainsString('Mutation Score Indicator (MSI): 100%', $output);
+    }
+}