diff --git a/src/Type/Accessory/AccessoryArrayListType.php b/src/Type/Accessory/AccessoryArrayListType.php
index ff3536f473..6042d14ced 100644
--- a/src/Type/Accessory/AccessoryArrayListType.php
+++ b/src/Type/Accessory/AccessoryArrayListType.php
@@ -162,6 +162,10 @@ public function setOffsetValueType(?Type $offsetType, Type $valueType, bool $uni
 
 	public function setExistingOffsetValueType(Type $offsetType, Type $valueType): Type
 	{
+		if ($this->hasOffsetValueType($offsetType)->no()) {
+			return new ErrorType();
+		}
+
 		return $this;
 	}
 
diff --git a/tests/PHPStan/Analyser/nsrt/bug-13629.php b/tests/PHPStan/Analyser/nsrt/bug-13629.php
new file mode 100644
index 0000000000..621b4169bb
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-13629.php
@@ -0,0 +1,37 @@
+<?php declare(strict_types = 1);
+
+namespace Bug13629;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @param array<string, list<array{xmlNamespace: string, namespace: string, name: string}>> $xsdFiles
+ * @param array<string, list<array{xmlNamespace: string, namespace: string, name: string}>> $groupedByNamespace
+ * @param array<string, list<string>> $extraNamespaces
+ */
+function test(array $xsdFiles, array $groupedByNamespace, array $extraNamespaces): void {
+	foreach ($extraNamespaces as $mergedNamespace) {
+		if (count($mergedNamespace) < 2) {
+			continue;
+		}
+
+		$targetNamespace = end($mergedNamespace);
+		if (!isset($groupedByNamespace[$targetNamespace])) {
+			continue;
+		}
+		$xmlNamespace = $groupedByNamespace[$targetNamespace][0]['xmlNamespace'];
+
+		assertType('string', $xmlNamespace);
+		assertType('non-empty-list<string>&hasOffsetValue(1, string)', $mergedNamespace);
+
+		$xsdFiles[$xmlNamespace] = [];
+		foreach ($mergedNamespace as $namespace) {
+			foreach ($groupedByNamespace[$namespace] ?? [] as $viewHelper) {
+				$xsdFiles[$xmlNamespace][$viewHelper['name']] = $viewHelper;
+			}
+		}
+		// After assigning with string keys ($viewHelper['name']), $xsdFiles[$xmlNamespace] should NOT be a list
+		assertType('array<int<0, max>, array{xmlNamespace: string, namespace: string, name: string}>', $xsdFiles[$xmlNamespace]);
+		$xsdFiles[$xmlNamespace] = array_values($xsdFiles[$xmlNamespace]);
+	}
+}
diff --git a/tests/PHPStan/Rules/Functions/ArrayValuesRuleTest.php b/tests/PHPStan/Rules/Functions/ArrayValuesRuleTest.php
index 1f3e273b16..37cb87b0f0 100644
--- a/tests/PHPStan/Rules/Functions/ArrayValuesRuleTest.php
+++ b/tests/PHPStan/Rules/Functions/ArrayValuesRuleTest.php
@@ -89,4 +89,9 @@ public function testFile(): void
 		$this->analyse([__DIR__ . '/data/array_values_list.php'], $expectedErrors);
 	}
 
+	public function testBug13629(): void
+	{
+		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-13629.php'], []);
+	}
+
 }