diff --git a/src/Type/Php/IsAFunctionTypeSpecifyingExtension.php b/src/Type/Php/IsAFunctionTypeSpecifyingExtension.php
index 4d062efd56..55789676aa 100644
--- a/src/Type/Php/IsAFunctionTypeSpecifyingExtension.php
+++ b/src/Type/Php/IsAFunctionTypeSpecifyingExtension.php
@@ -9,12 +9,9 @@
 use PHPStan\Analyser\TypeSpecifierAwareExtension;
 use PHPStan\Analyser\TypeSpecifierContext;
 use PHPStan\Reflection\FunctionReflection;
-use PHPStan\Type\ClassStringType;
 use PHPStan\Type\Constant\ConstantBooleanType;
 use PHPStan\Type\Constant\ConstantStringType;
 use PHPStan\Type\FunctionTypeSpecifyingExtension;
-use PHPStan\Type\ObjectWithoutClassType;
-use PHPStan\Type\TypeCombinator;
 use function count;
 use function strtolower;
 
@@ -50,14 +47,10 @@ public function specifyTypes(FunctionReflection $functionReflection, FuncCall $n
 		$allowStringType = isset($node->getArgs()[2]) ? $scope->getType($node->getArgs()[2]->value) : new ConstantBooleanType(false);
 		$allowString = !$allowStringType->equals(new ConstantBooleanType(false));
 
-		$superType = $allowString
-			? TypeCombinator::union(new ObjectWithoutClassType(), new ClassStringType())
-			: new ObjectWithoutClassType();
-
 		$resultType = $this->isAFunctionTypeSpecifyingHelper->determineType($objectOrClassType, $classType, $allowString, true);
 
 		// prevent false-positives in IsAFunctionTypeSpecifyingHelper
-		if ($resultType->equals($superType) && $resultType->isSuperTypeOf($objectOrClassType)->yes()) {
+		if ($classType->getConstantStrings() === [] && $resultType->isSuperTypeOf($objectOrClassType)->yes()) {
 			return new SpecifiedTypes([], []);
 		}
 
diff --git a/src/Type/Php/IsSubclassOfFunctionTypeSpecifyingExtension.php b/src/Type/Php/IsSubclassOfFunctionTypeSpecifyingExtension.php
index 0ca6cf4e76..71800c5366 100644
--- a/src/Type/Php/IsSubclassOfFunctionTypeSpecifyingExtension.php
+++ b/src/Type/Php/IsSubclassOfFunctionTypeSpecifyingExtension.php
@@ -9,12 +9,9 @@
 use PHPStan\Analyser\TypeSpecifierAwareExtension;
 use PHPStan\Analyser\TypeSpecifierContext;
 use PHPStan\Reflection\FunctionReflection;
-use PHPStan\Type\ClassStringType;
 use PHPStan\Type\Constant\ConstantBooleanType;
 use PHPStan\Type\FunctionTypeSpecifyingExtension;
 use PHPStan\Type\Generic\GenericClassStringType;
-use PHPStan\Type\ObjectWithoutClassType;
-use PHPStan\Type\TypeCombinator;
 use function count;
 use function strtolower;
 
@@ -51,14 +48,10 @@ public function specifyTypes(FunctionReflection $functionReflection, FuncCall $n
 			return new SpecifiedTypes([], []);
 		}
 
-		$superType = $allowString
-			? TypeCombinator::union(new ObjectWithoutClassType(), new ClassStringType())
-			: new ObjectWithoutClassType();
-
 		$resultType = $this->isAFunctionTypeSpecifyingHelper->determineType($objectOrClassType, $classType, $allowString, false);
 
 		// prevent false-positives in IsAFunctionTypeSpecifyingHelper
-		if ($resultType->equals($superType) && $resultType->isSuperTypeOf($objectOrClassType)->yes()) {
+		if ($classType->getConstantStrings() === [] && $resultType->isSuperTypeOf($objectOrClassType)->yes()) {
 			return new SpecifiedTypes([], []);
 		}
 
diff --git a/tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php b/tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php
index 896173a6ee..3236b7feee 100644
--- a/tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php
+++ b/tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php
@@ -1127,4 +1127,16 @@ public function testBug8954(): void
 		$this->analyse([__DIR__ . '/data/bug-8954.php'], []);
 	}
 
+	public function testBugPR3404(): void
+	{
+		$this->checkAlwaysTrueCheckTypeFunctionCall = true;
+		$this->treatPhpDocTypesAsCertain = true;
+		$this->analyse([__DIR__ . '/data/bug-pr-3404.php'], [
+			[
+				'Call to function is_a() with arguments BugPR3404\Location, \'BugPR3404\\\\Location\' and true will always evaluate to true.',
+				21,
+			],
+		]);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Comparison/data/bug-pr-3404.php b/tests/PHPStan/Rules/Comparison/data/bug-pr-3404.php
new file mode 100644
index 0000000000..7dd533ff98
--- /dev/null
+++ b/tests/PHPStan/Rules/Comparison/data/bug-pr-3404.php
@@ -0,0 +1,24 @@
+<?php // lint >= 8.0
+
+namespace BugPR3404;
+
+interface Location
+{
+
+}
+
+/** @return class-string<Location> */
+function aaa(): string
+{
+
+}
+
+function (Location $l): void {
+	if (is_a($l, aaa(), true)) {
+		// might not always be true. $l might be one subtype of Location, aaa() might return a name of a different subtype of Location
+	}
+
+	if (is_a($l, Location::class, true)) {
+		// always true
+	}
+};