diff --git a/rules-tests/CodeQuality/Rector/MethodCall/AssertCountWithZeroToAssertEmptyRector/Fixture/skip_union_type.php.inc b/rules-tests/CodeQuality/Rector/MethodCall/AssertCountWithZeroToAssertEmptyRector/Fixture/skip_union_type.php.inc
new file mode 100644
index 00000000..f174f98c
--- /dev/null
+++ b/rules-tests/CodeQuality/Rector/MethodCall/AssertCountWithZeroToAssertEmptyRector/Fixture/skip_union_type.php.inc
@@ -0,0 +1,14 @@
+<?php
+
+namespace Rector\PHPUnit\Tests\CodeQuality\Rector\MethodCall\AssertCountWithZeroToAssertEmptyRector\Fixture;
+
+final class SkipUnionType extends \PHPUnit\Framework\TestCase
+{
+    public function test($something)
+    {
+        foreach ([true, false] as $value) {
+            $count = (int) $value;
+            $this->assertCount($count, $something);
+        }
+    }
+}
diff --git a/rules/CodeQuality/Rector/MethodCall/AssertCountWithZeroToAssertEmptyRector.php b/rules/CodeQuality/Rector/MethodCall/AssertCountWithZeroToAssertEmptyRector.php
index 16cb96f3..48c822d8 100644
--- a/rules/CodeQuality/Rector/MethodCall/AssertCountWithZeroToAssertEmptyRector.php
+++ b/rules/CodeQuality/Rector/MethodCall/AssertCountWithZeroToAssertEmptyRector.php
@@ -8,6 +8,7 @@
 use PhpParser\Node\Expr\MethodCall;
 use PhpParser\Node\Expr\StaticCall;
 use PhpParser\Node\Name;
+use PHPStan\Type\UnionType;
 use Rector\PHPUnit\NodeAnalyzer\TestsNodeAnalyzer;
 use Rector\Rector\AbstractRector;
 use Symplify\RuleDocGenerator\ValueObject\CodeSample\CodeSample;
@@ -69,6 +70,11 @@ public function refactor(Node $node): MethodCall|StaticCall|null
         }
 
         $type = $this->getType($node->getArgs()[0]->value);
+
+        if ($type instanceof UnionType) {
+            return null;
+        }
+
         $value = ($type->getConstantScalarValues()[0] ?? null);
         if ($value === 0) {
             $args = $node->getArgs();