diff --git a/src/Psalm/Internal/Analyzer/Statements/Expression/AssertionFinder.php b/src/Psalm/Internal/Analyzer/Statements/Expression/AssertionFinder.php
index f83203e7a..62dc691c7 100644
--- a/src/Psalm/Internal/Analyzer/Statements/Expression/AssertionFinder.php
+++ b/src/Psalm/Internal/Analyzer/Statements/Expression/AssertionFinder.php
@@ -2296,11 +2296,11 @@ class AssertionFinder
         if ($stmt->name instanceof PhpParser\Node\Name
             && strtolower($stmt->name->parts[0]) === 'class_exists'
         ) {
-            if (!isset($stmt->args[2])) {
+            if (!isset($stmt->args[1])) {
                 return true;
             }
 
-            $second_arg = $stmt->args[2]->value;
+            $second_arg = $stmt->args[1]->value;
 
             if ($second_arg instanceof PhpParser\Node\Expr\ConstFetch
                 && $second_arg->name instanceof PhpParser\Node\Name
diff --git a/tests/ClassTest.php b/tests/ClassTest.php
index 273ecd5f1..151266808 100644
--- a/tests/ClassTest.php
+++ b/tests/ClassTest.php
@@ -391,7 +391,7 @@ class ClassTest extends TestCase
                         if (class_exists($s) || interface_exists($s)) {}
                     }'
             ],
-            'SKIPPED-classExistsWithFalseArg' => [
+            'classExistsWithFalseArg' => [
                 '<?php
                     /**
                      * @param class-string $class