diff --git a/src/Psalm/Internal/Type/TypeCombiner.php b/src/Psalm/Internal/Type/TypeCombiner.php
index 0132e4e6bf4..89abc13b52c 100644
--- a/src/Psalm/Internal/Type/TypeCombiner.php
+++ b/src/Psalm/Internal/Type/TypeCombiner.php
@@ -676,7 +676,11 @@ private static function scrapeTypeProperties(
 
                 if (!$candidate_property_type->possibly_undefined) {
                     $has_defined_keys = true;
-                } elseif ($combination->fallbackKeyContains($candidate_property_name)) {
+                }
+
+                if (($candidate_property_type->possibly_undefined || ($value_type->possibly_undefined ?? true))
+                    && $combination->fallbackKeyContains($candidate_property_name)
+                ) {
                     $combination->objectlike_entries[$candidate_property_name] = Type::combineUnionTypes(
                         $combination->objectlike_entries[$candidate_property_name],
                         $combination->objectlike_value_type,
diff --git a/tests/TypeCombinationTest.php b/tests/TypeCombinationTest.php
index 071b4b8d617..f116e3703a9 100644
--- a/tests/TypeCombinationTest.php
+++ b/tests/TypeCombinationTest.php
@@ -7,6 +7,8 @@
 use Psalm\Type;
 use Psalm\Type\Atomic;
 
+use function array_reverse;
+
 class TypeCombinationTest extends TestCase
 {
     use ValidCodeAnalysisTestTrait;
@@ -30,6 +32,11 @@ public function testValidTypeCombination(string $expected, array $types): void
             $expected,
             TypeCombiner::combine($converted_types)->getId(),
         );
+
+        $this->assertSame(
+            $expected,
+            TypeCombiner::combine(array_reverse($converted_types))->getId(),
+        );
     }
 
     public function providerValidCodeParse(): iterable
@@ -90,6 +97,20 @@ function expectsTraversableOrArray($_a): void
     public function providerTestValidTypeCombination(): array
     {
         return [
+            'complexArrayFallback1' => [
+                'array{other_references: list<Psalm\Internal\Analyzer\DataFlowNodeData>|null, taint_trace: list<array<array-key, mixed>>|null, ...<string, mixed>}',
+                [
+                    'array{other_references: list<Psalm\Internal\Analyzer\DataFlowNodeData>|null, taint_trace: null}&array<string, mixed>',
+                    'array{other_references: list<Psalm\Internal\Analyzer\DataFlowNodeData>|null, taint_trace: list<array<array-key, mixed>>}&array<string, mixed>',
+                ],
+            ],
+            'complexArrayFallback2' => [
+                'list{0?: 0|a, 1?: 0|a, ...<int<0, max>, a>}',
+                [
+                    'list<a>',
+                    'list{0, 0}',
+                ],
+            ],
             'intOrString' => [
                 'int|string',
                 [