diff --git a/src/Psalm/Internal/Analyzer/Statements/Expression/Assignment/ArrayAssignmentAnalyzer.php b/src/Psalm/Internal/Analyzer/Statements/Expression/Assignment/ArrayAssignmentAnalyzer.php
index 1b64ce3805f..f1890d3ded1 100644
--- a/src/Psalm/Internal/Analyzer/Statements/Expression/Assignment/ArrayAssignmentAnalyzer.php
+++ b/src/Psalm/Internal/Analyzer/Statements/Expression/Assignment/ArrayAssignmentAnalyzer.php
@@ -650,17 +650,18 @@ private static function updateArrayAssignmentChildType(
                     } else {
                         assert($array_atomic_type_list !== null);
                         $array_atomic_type = new TKeyedArray(
-                            array_fill(
+                            [...array_fill(
+                                $atomic_root_type_array->getMinCount(),
+                                count($atomic_root_type_array->properties)-1,
+                                $array_atomic_type_list
+                            ), ...array_fill(
                                 0,
-                                count($atomic_root_type_array->properties),
-                                $array_atomic_type_list,
-                            ),
+                                count($atomic_root_type_array->properties)-1,
+                                Type::getNever()
+                            )],
                             null,
-                            [
-                                Type::getListKey(),
-                                $array_atomic_type_list,
-                            ],
-                            true,
+                            null,
+                            true
                         );
                     }
                     $from_countable_object_like = true;
diff --git a/src/Psalm/Type/Atomic/TKeyedArray.php b/src/Psalm/Type/Atomic/TKeyedArray.php
index df48a09e3f6..11a1ccf4a89 100644
--- a/src/Psalm/Type/Atomic/TKeyedArray.php
+++ b/src/Psalm/Type/Atomic/TKeyedArray.php
@@ -85,6 +85,19 @@ public function __construct(
         $this->fallback_params = $fallback_params;
         $this->is_list = $is_list;
         $this->from_docblock = $from_docblock;
+        if ($this->is_list) {
+            $last_k = -1;
+            $had_possibly_undefined = false;
+            ksort($this->properties);
+            foreach ($this->properties as $k => $v) {
+                if (is_string($k) || $last_k !== ($k-1) || ($had_possibly_undefined && !$v->possibly_undefined)) {
+                    $this->is_list = false;
+                    break;
+                }
+                $had_possibly_undefined = $v->possibly_undefined || $had_possibly_undefined;
+                $last_k = $k;
+            }
+        }
     }
 
     /**
@@ -98,6 +111,19 @@ public function setProperties(array $properties): self
         }
         $cloned = clone $this;
         $cloned->properties = $properties;
+        if ($cloned->is_list) {
+            $last_k = -1;
+            $had_possibly_undefined = false;
+            ksort($cloned->properties);
+            foreach ($cloned->properties as $k => $v) {
+                if (is_string($k) || $last_k !== ($k-1) || ($had_possibly_undefined && !$v->possibly_undefined)) {
+                    $cloned->is_list = false;
+                    break;
+                }
+                $had_possibly_undefined = $v->possibly_undefined || $had_possibly_undefined;
+                $last_k = $k;
+            }
+        }
         return $cloned;
     }
 
diff --git a/tests/ArrayAccessTest.php b/tests/ArrayAccessTest.php
index 2ea42045234..7538885ef76 100644
--- a/tests/ArrayAccessTest.php
+++ b/tests/ArrayAccessTest.php
@@ -433,6 +433,44 @@ function foo(array $a, int $b): void {
     public function providerValidCodeParse(): iterable
     {
         return [
+            'testBuildList' => [
+                'code' => '<?php
+                    $a = [];
+
+                    if (random_int(0, 1)) {
+                        $a []= 0;
+                    }
+
+                    if (random_int(0, 1)) {
+                        $a []= 1;
+                    }
+
+                    $pre = $a;
+
+                    $a []= 2;
+
+                ',
+                'assertions' => [
+                    '$pre===' => 'list{0?: 0|1, 1?: 1}',
+                    '$a===' => 'list{0: 0|1|2, 1?: 1|2, 2?: 2}',
+                ]
+            ],
+            'testBuildListOther' => [
+                'code' => '<?php
+                    $list = [];
+                    $entropy = random_int(0, 2);
+                    if ($entropy === 0) {
+                        $list[] = "A";
+                    } elseif ($entropy === 1) {
+                        $list[] = "B";
+                    }
+
+                    $list[] = "C";
+                ',
+                'assertions' => [
+                    '$list===' => "list{0: 'A'|'B'|'C', 1?: 'C'}"
+                ]
+            ],
             'instanceOfStringOffset' => [
                 'code' => '<?php
                     class A {