diff --git a/PhpCollective/Sniffs/Classes/Psr4Sniff.php b/PhpCollective/Sniffs/Classes/Psr4Sniff.php
index 45c0564..64ad216 100644
--- a/PhpCollective/Sniffs/Classes/Psr4Sniff.php
+++ b/PhpCollective/Sniffs/Classes/Psr4Sniff.php
@@ -9,6 +9,7 @@
 
 namespace PhpCollective\Sniffs\Classes;
 
+use InvalidArgumentException;
 use PHP_CodeSniffer\Config;
 use PHP_CodeSniffer\Files\File;
 use PHP_CodeSniffer\Sniffs\Sniff;
@@ -100,11 +101,16 @@ protected function initializeThisSniffIfNotYet(Config $config): void
     {
         if ($this->initialization === static::UNINITIALIZED) {
             $this->initialization = static::INITIALIZATION_FAILURE;
-            $this->autoloadabilityInspectors =
-                AutoloadabilityInspectorsFactory::create(
-                    $config->getSettings()['basepath'] ?: getcwd(),
-                    $this->composerJsonPath,
-                );
+            try {
+                $this->autoloadabilityInspectors =
+                    AutoloadabilityInspectorsFactory::create(
+                        $config->getSettings()['basepath'] ?: getcwd(),
+                        $this->composerJsonPath,
+                    );
+            } catch (InvalidArgumentException) {
+                // Missing or unreadable composer.json: nothing to check against. Invalid JSON still throws.
+                return;
+            }
             $this->initialization = static::INITIALIZED;
         }
     }
diff --git a/tests/PhpCollective/Sniffs/Classes/Psr4SniffTest.php b/tests/PhpCollective/Sniffs/Classes/Psr4SniffTest.php
new file mode 100644
index 0000000..d46e617
--- /dev/null
+++ b/tests/PhpCollective/Sniffs/Classes/Psr4SniffTest.php
@@ -0,0 +1,25 @@
+<?php
+
+/**
+ * MIT License
+ * For full license information, please view the LICENSE file that was distributed with this source code.
+ */
+
+namespace PhpCollective\Test\PhpCollective\Sniffs\Classes;
+
+use PhpCollective\Sniffs\Classes\Psr4Sniff;
+use PhpCollective\Test\TestCase;
+
+class Psr4SniffTest extends TestCase
+{
+    /**
+     * @return void
+     */
+    public function testMissingComposerJsonDisablesSniff(): void
+    {
+        $sniff = new Psr4Sniff();
+        $sniff->composerJsonPath = 'does-not-exist/composer.json';
+
+        $this->assertSnifferFindsErrors($sniff, 0);
+    }
+}
diff --git a/tests/_data/Psr4/before.php b/tests/_data/Psr4/before.php
new file mode 100644
index 0000000..d5f03cd
--- /dev/null
+++ b/tests/_data/Psr4/before.php
@@ -0,0 +1,7 @@
+<?php declare(strict_types = 1);
+
+namespace PhpCollective;
+
+class FixMe
+{
+}